UNITED KINGDOM (continue)

5. HYDROGRAPHY AND LIMNOLOGY

A recent (1991) official estimate of the extent of inland waters in the United Kingdom and its major divisions is given in Table 1. Following this Table, the UK as a whole has 3 218 km² of inland waters, i.e., only 1.3 percent of its total area (see Table 15 which is in essential agreement). Inland water constitutes only 0.58 percent of the total area of England, 0.62 percent of the total area of Wales, 2.15 percent of Scotland's total area, and 4.5 percent of Northern Ireland. In an earlier paper, Smith and Lyle (1979) presented, for the waters of Great Britain only, somewhat different figures (see Table 3). They do, however, agree generally with those in Table 1¹.

¹ Scotland (1990) also differs somewhat in claiming for Scotland a total area of 78 783 km² including 1 703 km² of inland waters (2.16 percent of the total)

Table 3

Water surface areas in Great Britain

Source: Smith and Lyle (1979)

Van der Leeden (1975) gives the approximate annual runoff in the UK as 508 mm, and both he and ECE (1978) list the total discharge of the UK rivers as 122 thousand million m³ annually. During the period of 1916–50, when the average annual runoff for the UK was 128 778 million m³, the runoff from Scotland was 70.231 million m³ (54 percent of the entire UK), that from England and Wales was 50 thousand million m³ (39 percent), and that from Northern Ireland, 8 547 million m³ (7 percent) according to Central Water Planning Unit, Department of the Environment (1978).

Some relationships between rainfall, runoff, and discharge in major river basins of the UK are shown in Table 4.

Table 4

Relationship of rainfall to runoff and discharge in 14 major river basins in the UK

Source: UK/EIFAC (1975, 1979)

As noted in section 3, the waters of Highland and Lowland Britain differ generally in their physicochemical characteristics which in turn determine their biological attributes. Thus, for example, upland streams draining moorlands may have a pH of 6 or less and a total hardness below 20 mg/l is likely. On the other hand, a typical chalk water in the lowlands may have a pH of 8 or over and perhaps 40 mg/l total hardness (Smith, 1972). Table 5 illustrates some of these differing characteristics, generally, and Table 6 illustrates some of the chemical differences specifically.

Table 5

Some characteristics of “Highland” and “Lowland” waters

Source: Natural Environment Research Council (1972)

5.1 Rivers

As would be expected, estimates of the number and length of rivers in the UK vary widely, being dependent not only upon the scale of map or aerial photo used for the calculation, or the assiduity of the field observer, but upon the presentation of such statistics by different authors or agencies. Thus, Holden and Lloyd (1972) list the length of the rivers in the UK as 42 800 km. The Travis Commission (1980) states that the UK has 35 950 km of non-tidal rivers with a dry weather flow of at least 4 550 m³/day and another 2 870 km of tidal rivers, a total of 38 820 km. Ward (1981) estimates a total river length in Great Britain of 58 380 km. UK/EIFAC (1979) says that the rivers of Scotland alone can be estimated at 47 772 km. Tombleson (1982) states that in England and Wales alone there are 40 000 km of non-tidal rivers and 3 200 km of tidal rivers, and that in Northern Ireland there are approximately 2 112 km of rivers. With respect to numbers, Smith and Lyle (1979) have estimated that in Great Britain alone there are 1 445 river systems, each draining about 159 km², and a total of 194 674 individual streams.

Regardless of such estimates, it is apparent that while the UK is drained by many rivers, its size and dimensions preclude the existence of many that are long, have large catchments, or have high flows. Table 7 shows the major British rivers ranked in terms of these dimensions. It will be noted that this Table from a recent definitive work has some figures which differ quite a bit from those given by other authors. For example, a number of other authorities list the three longest rivers in England as the Severn, Thames and Trent, and claim the Tay as the longest river in Scotland with the Spey and Clyde almost tied for second place. (The general size of these rivers is well known; it is futile to spend time here analysing the reasons for such differences in opinion.)

Table 6

Examples of water quality in Great Britain

Source: Table 1 of Templeton (1984)

Despite their relatively small size, a number of British rivers have large concentrations of water in their estuaries. Tidal scour in the UK makes for estuaries rather than deltas, and navigability is also a feature of many British rivers. Because of the higher land mass towards the west, most of the longer rivers of Great Britain flow eastward into the North Sea. They are more sluggish than those flowing westward, of which only the Wye, Severn and Clyde have a considerable length.

In Great Britain, proceeding clockwise from the north, the principal rivers or drainages are listed below. On the east coast in Scotland, the Spey, Deveron, Don, Dee, Tay (with its tributaries, the Garry and Tummel), Forth and Tweed (part of the boundary with England) are all fast-flowing rivers, coursing over impenetrable rocks and responsive to rain.

Farther south, the Tyne, Wear and Tees run eastward from the Pennines to the North Sea. Below these is the most northerly of the major estuarine groupings, the Swale, Ure, Nidd, Wharfe, Aire, Calder and Don, all of which ultimately reach the Humber through the Ouse. The Humber is also joined from the south by the chief river of the Midlands, the Trent, whose tributaries include the Tame, Dove (Izaak Waltons' stream), Derwent, Soar, Erewash, Devon and Idle. This group represents about 25 000 km² or about one-fifth of England's watershed.

Next south are a number of drainages, including the Witham, Welland, Nene and Great Ouse, which descend into the Fens (low-lying drained country), and then pass into the drowned plain of the Wash, a shallow estuarine inlet of the North Sea.

Table 7

Major British rivers ranked in terms of length, basin area and discharge

Source: Table 1.1 of Ward (1981)

The last large river on the eastern coast of Great Britain is the Thames¹. Dominating the southeast of England, and forming the port of London, it is England's principal river, the longest in Great Britain and the one with the largest drainage basin.

¹ Although the Thames ranks as the greatest river in Great Britain, it ranks far below such great rivers of Europe as the Danube (2 740 km long, drainage basin of 816 000 km², and mean annual flow of 7 000 m³/sec), or the Rhine (1 320 km long, drainage basin of 160 000 km², and a mean annual flow of 2 000 m³/sec)

Tributaries include the Lea, Wey, Mole, and Kennet, and its estuarine or tidal portion is about 150 km long. The total fall of the Thames in 239 km is only 113 m, but in the last century the river was provided with many weirs and locks, at intervals of about 5 km, to maintain a constant depth of water (minimum 2 m) for navigation. With a catchment containing much chalk and limestone, the river water is hard. It has a calcium content of about 100 mg/l and has high productivity (see section 9.1). The Thames is an excellent example of a British river subjected to the demands of millions of people. At one time it was so grossly polluted by sewage and industrial effluent that its formerly abundant estuarine and migratory fishes were decimated. Circa 1964, it was reported that the river for at least 50km was completely anerobic from surface to bottom for at least one month in summer. However, estuarine conditions have been so improved by rigorous pollution control that it can again support salmon (Mann, 1972). The Thames also supports more angling and pleasure boating than any other river in the UK. Recently a new barrier system has been erected at Woolwich, to prevent flooding in London at times when equinoctial spring tides may coincide with a tidal surge in the North Sea. This barrier normally lies on the bottom of the river to be raised only in time of emergency, but aside from the tidal factor, London and the southeast of England are sinking at a rate of about one-third of a centimetre per year, and there have been pressures to make such a barrier permanent. Should this be done, it might augment river heat, siltation and pollution, and prevent fish migration according to Wheeler (1979).

The southern coast of England borders the English Channel. Most of the rivers entering here are short, independent streams. Proceeding clockwise, they include the: Rother, Arun, Itchen, Test, Hampshire, Avon, Stour, Exe, Dart and Tamar. The Test and Itchen are two of England's most famous chalk streams, well steeped in angling lore.

On the west coast of Great Britain, the largest drainage complex is that containing the Severn and Wye, covering about three-quarters of Wales and part of England. The Severn, Teme and Warwickshire Avon are the major rivers of its upper basin, while the Wye, Usk, Bristol Avon, and Parrett flow into the estuary or Bristol Channel. The Severn is connected by canals with the Thames, Mersey and Trent.

With the exception of this complex, most of the other west coast rivers are short streams which reach the Atlantic quickly.

There are only a few other major western rivers: the Tywi and Dee in Wales; the Mersey, Ribble and Lune in England; and the Nith and Clyde in Scotland. These, generally, complete the “clockwise” complement of rivers in Great Britain.

In Northern Ireland, again proceeding clockwise from the north, the principal streams are as follows. The Erne, rising in Lough Gowna, flows 135 km to Donegal Bay in the Republic of Ireland through Upper and Lower Lough Ernes. Draining western North Ireland is the Foyle system. The Foyle, formed by the union of the 40-km Finn from the Republic of Ireland to the west and the northerly flowing Mourne, flows 26 km to Lough Foyle, as 32-km inlet of the Atlantic. Draining the centre of Northern Ireland is the Bann/Lough Neagh system. The Upper Bann River flows north 64 km to enter Lough Neagh, and as its outlet, the Lower Bann continues north for another 64 km to debouch in the Atlantic. Other principal streams feeding Lough Neagh are the Moyola, Ballinderry, Blackwater and Main.

Tables 4, 7 and 8 show the discharge of some of UK's principal rivers. (The UK with its abundant water resources, had a later start in establishment of flow-gauging stations than several of the continental countries. In 1935–36, Great Britain had only 27 gauging stations. By 1974, it had 1 205 stations (Ward, 1981).)

In the UK, where rainfall is rather consistent from month to month, the flow regime is generally a simple one. The maximum discharge is during the winter when evaporation is low and soil moisture and ground water high; the minimum flow is during summer when the opposite characteristics prevail. Within this broad pattern most of the northern and western streams have a maximum flow in December while central and eastern English streams have a peak in January and February. In parts of Scotland there may be a secondary maximum from snowmelt in March or April.

Table 8

Discharge of twelve major rivers in the UK^a

^a Not represented here is the Tay, in Scotland, the UK river with the largest mean annual flow, 152.2 m³/s up to about 1981

Source: Van der Leeden (1975) after Unesco (1971), and A. Willis (1973), data on discharge of principal rivers, Water Resources Board, Reading (private communication)

Those rivers having their source high in the hills are generally quite variable in flow; those originating in springs are more constant. However, the installation of impoundments on many hill streams has reduced the amount of maximum flow and provided compensation water to increase the flow at times of drought. Conversely, some spring-fed streams have been subject to increased maximum flows due to the greater extent of contiguous paved areas.

Water temperature is also more variable, both diurnally and annually, in the streams having a high source, while spring-fed waters have a remarkably even temperature. Generally speaking, the water temperatures of the larger rivers (and lakes) are neither very low nor very high, and throughout Britain are generally suitable for salmonoid fishes. River temperatures in the UK rarely exceed 25°C under natural conditions, and the upper limit is normally about 16–22°C depending upon latitude and altitude (Walling and Webb, 1981). Most are usually below 6°C in winter, and even a chalk stream such as the Test has varied from 2.2°C to 19.5°C. Typical characteristics of the thermal pattern of British rivers are shown in Table 9. Both impoundment and the entrance of hot water from cooling systems have, however, altered water temperatures, e.g., by as much as 10°C.

Water clarity varies from that of crystalline small hill streams to that of the large low-lying tidal rivers (e.g., Severn, Wash and Humber) which carry large quantities, of sediment.

British streams have been classified in various ways according to their elevation, gradient, substratum, vegetation and fish or invertebrate fauna. (Emphasis in this review is on fish and fisheries, hence the examples of stream classification selected. For a classification of running water sites in Great Britain using macro-invertebrates, see Wright et al., 1984.) An old but rather widely accepted classification based on the dominant fish species (Carpenter, 1928) divides a typical river into the following zones:

1. “Headstream” or “highland brook” - small, often torrential, and without fish or with salmon and trout parr only;

2. “Troutbeck” - larger, more constant but still torrential, rocky, with trout as the only permanent residents of open water but with bullheads (Cottus gobio) among the stones;

3. “Minnow reach” - fairly swift, silt and mud in a few places, some rooted plants, and trout, salmon and minnows (Phoxinus phoxinus) common;

4. “Lowland reach” - slow moving, muddy bottom with vegetation, and with coarse fish (primarily cyprinids) present.

Table 9

Characteristics typical of the thermal regimes of British rivers

Source: Smith (1979)

Obviously, not every river possesses each of these zones. Some do not rise in hills, and others have alternating riffles and pools or even reversed stretches. The first two zones are typical of the mountains and moorlands of Scotland, Wales and northern and western England. The two latter zones are found typically in the Midlands and south of England.

To these four types of stream, one might add a fifth, the famous spring-fed chalk streams, with rather constant flow and temperature, calcareous, with abundant vegetation and good populations of trout (e.g., Test, Hampshire, Avon and Itchen).

Similar classifications have been made of continental streams, especially by Huet (1949, 1954) whose “grayling zone” corresponds to Carpenter's “minnow reach, and his “barbel” and “bream” zones to the “lowland reach” (see section 5.1 of the reviews of Belgium and France). Hawkes (1975), while retaining Huet's general classification, has included some alternative fishes as more suitable key species for British streams. His system in abbreviated and somewhat modified form follows:

1. “Trout zone” - salmonids, bullheads, minnow;

2. “Minnow or grayling zone” - mixed fauna with salmonids dominant plus rhaeophilic cyprinids (e.g., chub and barbel);

3. “Chub or barbel zone” - mixed fauna with cyprinids dominant, including rhaeophilic cyprinids plus roach, rudd and dace;

4. “Bream zone” - cyprinids, especially limnophilic forms such as bream, carp and dace, plus predators such as pike, perch and eel.

5.2 Lakes

Smith and Lyle (1979) have made a count of 5 502 lakes and reservoirs in Great Britain, calculating their total area as 1 924.3 km² or 80 percent of the island's inland water area. See Table 3 for their estimates of lake area. They further state that there are 3 778 lochs in Scotland alone, but that 78 percent of them are less than 0.25 km² in area.

With respect to Scotland alone, Maitland (1981) states that it possesses about 3 800 lakes (lochs) over 4 ha in area, representing 69 percent of the British total, and that a comparable figure for England and Wales is 1 700 lakes. There are at least 25 lochs in Scotland with a surface area exceeding 8 km². Scotland also possesses the largest number of very small static water bodies in the UK. Some authors consider that it may have as many as 10 000 lochs, lochans and tarns. By contrast, England and Wales have relatively few lakes (Ilyns in Wales) and about 52 km² of these are concentrated in England's lake District. Northern Ireland has over 200 small lakes and a number of large ones (called loughs).

Most of the lakes in the UK are products of glaciation. Some of these are only a few hectares in extent, e.g., the little rock or moraine tarns of Upland Britain, nestled in cirques (the corries of the Highlands or cwms of Wales). Many are of far greater extent: the ribbon lakes of the Lake District and the deep glen lochs of Scotland's highlands, also excavated by glaciers in rock basins. There are also some lowland lakes such as the shallow Loch Leven lying in the hollows of glacial debris. Gorham (1958) states that of 399 lakes in Scotland examined by a survey in 1897–1909, 262 represent rock basins and 137 are basins lying in or at least dammed by glacial drift. A few lakes in the UK are at least partially tectonic in origin. Loch Ness, with a mean depth (132 m) greater than that of any other British lake, appears to be a glacier-excavated and tectonically depressed lake. On the other hand, Lough Neagh in Northern Ireland, with a mean depth of only 11.5 m, is a partial product of sagging and faulting. Finally, another large expanse of static water (12 km²), the Norfolk Broads, apparently represents an area of flooded medieval peat diggings.

Most of the natural lakes in Scotland, Ireland, and the Lake District, being affected by the oceanic climate, are warm monomictic, i.e., with a winter circulation at or above 4°C and direct stratification in the summer. Gorham (1958) states that in Scotland the lakes are beginning to warm up and stratify by April, with the smallest and shallowest lochans reaching temperatures of 7–10°C while the largest and deepest lochs remain at about 5°C. From June to August the small lochans maintain their surface temperatures a little above 13°C while the big lochs warm up gradually to this temperature. Bottom temperatures at this time are only slightly lower in the shallow lochans (mean depth about 1.5 m) while in the deepest lochs (mean depth greater than 76 m) they remain around 4–5°C. By October, surface temperatures are falling in all the lakes while those up to about 1.3 km² and 15 m mean depth are nearly isothermal. Many of the Scottish lochs become ice-covered for short periods, though few large ones are iced over for long. Laird and Needham (1988) say that any small loch (i.e., no greater in area than about 15 ha) in northern Scotland can expect icecover which will last one to four months.

The deep lakes generally lie in upland or mountainous country, have rocky shores, and populations of brown trout (Salmo trutta) and char (Salvelinus alpinus). Those at lower elevations with more littoral areas contain mixed fish populations including pike (Esox lucius) and European perch (Perca fluviatilis). Lakes in the lowlands surrounded by agricultural areas are shallow and have cyprinid stocks.

Some of the better known lakes in the UK are mentioned below.

Scotland. A bathymetrical survey of Scotland's freshwater lochs initiated by Sir John Murray in 1897 (Murray and Pullar, 1910) is considered a classic of limnology. The morphometry of 20 of the largest of these lochs, based primarily on their data, is shown in Table 10.

Loch Lomond, 36.4 m long, 8 km wide and 71.1 km² in extent, is the largest lake in area in Great Britain. However, Loch Ness, 56.4 km² in area, and forming about two-fifth's of the Caledonian Canal (see section 5.4), is the island's largest take in volume, 7 452 million m³, and with a maximum depth of 229.8 m is its second deepest lake. In fact, Loch Ness contains more water than all the lakes and reservoirs in England and Wales put together. Loch Morar, with a maximum depth of 310.3 m is its deepest lake. It is also the seventh deepest in Europe and seventeenth deepest in the world. The longest lake in Great Britain is Loch Awe, 41 km long but only about 1 km in breadth in most places. All of these lakes are temperate dimictic, oligotrophic, and nutrient-poor. Differing from these Highland or glen lochs is the productive, polymictic Loch Leven, 13.7 Km² in area, with a maximum depth of 25 m and a mean depth of only 4.5 m. The fish fauna in these large lakes ranges from only five species in Loch Morar and Shiel to 15 species in Loch Lomond.

England and Wales. By far the largest group of natural lakes in either England or Wales are the 15 that lie in the Lake District in northwest England. Thirteen of these total 51.77 km² in area. Table 11 shows their morphometry. Data for the first 10 lakes in this table is from Mill (1895), a classical limnological study made from a rowboat. The largest of these lakes, Windermere, with an area of 14.8 km² and volume of 347 million m³ is also the largest lake in England. The deepest lake in the District is Wastwater, with a maximum depth of 78.6 m and average depth of 41.0 m. These lakes seldom freeze, and all are monomictic except Esthwaite Water and Blelham Tarn which are occasionally dimictic, and the polymictic Bassenthwaite Water. Some of their characteristics are shown in Table 12. They are generally soft-water lakes; e.g., using Ca as an indicator, the highest in the district is Esthwaite (8.3 mg/l), the lowest is Thirlmere (3.3 mg/l), and the average is 4.5 mg/l. Thirlmere and Haweswater have been modified by dams for water supply for about 80 years. The fish fauna of these lakes is a small one. Some of the principal species are brown trout, char, pike, perch and the minnow (Phoxinus phoxinus), salmon also run through some of the lakes. See especially Macan (1970, 1984) for detailed descriptions.

Table 10

Morphometry of the twenty largest lakes in Scotland

Source: Maitland (1981) for almost all figures

Table 11

Morphometry of the English lakes

^a Before it became a reservoir
^b Does not include the drainage areas of Derwestwater and Thirlmere

Source: Macan (1970)

Table 12

Characteristics of selected lakes in the English Lake District

^a Windermere has North and South basins

Source: Goldman and Horne (1983) after Macan (1970) and Heron (1961)

There are no large natural lakes in the English lowlands; most are man-made. One of the most remarkable of these complexes is the Norfolk Broads, a group of 40 small, shallow (1–2 m) lakes from 10 to 120 ha in size, connected by channels to the rivers. The basins were excavated by man some few hundred years prior to the fourteenth and fifteenth centuries in order to obtain peat. Subsequently flooded, they formed static waters, and digging continued to connect the basins with rivers (Lambert et al., 1960). Heavy nutrification from sewage and aquatic birds has caused severe changes since the 1930s: turbidity, loss of macrophytes and fish kills by the brackishwater flagellate Prymnesium parvum (Moss, 1978).

Highland Wales has a number of lake areas but some have been greatly modified for water supply. The largest natural lake in Wales is the 1.7-km² Llyn Bala or Tegid on the Dee.

Table 13 shows the extent of lake and reservoir waters in England and Wales.

Table 13

Areas of inland waters in England and Wales

Source: National Environment Research Council (1972)

Northern Ireland. With a catchment that is 32 percent of Northern Ireland, Lough Neagh is by far the largest lake in the British Isles. With an area of 388.5 km², it is more than twice as large as the Republic of Ireland's largest lake, Lake Corrib (168.5 m²), about five times the size of Loch Lomond, and 25 times the size of Windermere. Although the temperature rarely rises above 20°C, this is an extremely rich, almost hypereutrophic lake, unusual in being well mixed and well oxygenated at all levels. Highly nutrified it is rich in both plankton and bottom fauna. Some of its characteristics are shown in Table 14. Lough Neagh supports a mixed fish fauna of salmonids and “coarse” fishes, augmented by runs of salmon (Salmo salar) and European eel (Anguilla anguilla) from the sea through its outlet the River Bann. Of particular interest is its abundant population of the pollan, lately termed Coregonus autumnalis pollan by Ferguson, Himberg, and Svardson (1978), and apparently unique in being the only coregonine of the cisco group in Western Europe¹.

¹ O'Grady (1988) calls this pollan C. alba [probably C. albula]

Table 14

Characteristics of Lough Neagh, Northern Ireland

Source: Milway (1970), Govt. of Northern Ireland (1970)

Brown trout also form a commercial fishery and salmon are important in the drainage. The most valuable modern fishery, however, is the eel caught both in the lake and in its outlet (see section 7.1.1). There are also abundant supplies of bream (Abramis brama), gudgeon (Gobio gobio), perch and pike. Aside from fishing, the lake is used for sewage and industrial disposal and water extraction.

The Upper and Lower Lough Ernes, totalling 140 km², are other large Northern Ireland lakes; they also contain “pollan” as do the Shannon Lakes of the Republic of Ireland (Wilson and Pitcher, 1983).

5.3 Reservoirs

Table 13 shows that circa 1972 there were 152 km² of reservoirs and 28 km² of wet gravel pits in England and Wales alone. The Travis Commission (1980) said that in 1977 a survey recognized 537 reservoirs of 2 ha or more in England and Wales with a total surface area of over 202.5 km². The Commission also estimated that there were about 750 gravel pits of 2 ha or over in England and Wales. Tombleson (1982) says that England and Wales possess 220 km² of water system reservoirs. These include the 12.5 km² Rutland Water, then the largest reservoir in the UK, which opened to trout fishing in 1976 and sold 33 000 day-permits in 1979. Since then, the Kielder Reservoir in the UK has been filled to become one of Europe's largest reservoirs. Separate area figures for reservoirs in Scotland and Northern Ireland are not available to the author. However, in Scotland reservoirs are included with natural lakes used for water supply, and Mills (1980) states that up to 1971 Scotland had a total of 380 reservoirs and lochs developed for water resources for public supply. In Wales much of the lotic water is man-made or has been modified for use as power or water supply, and the Welsh Dee with three large upland storage reservoirs is among the most comprehensively regulated rivers in Britain. Natural lakes in England have also been modified for water use, e.g., Haweswater was enlarged to furnish water to Manchester. Circa 1973, the quantity of water stored in the English and Welsh reservoirs represented about two percent of an average year's runoff. Offstream reservoirs are generally preferred, and the trend is to increase their size. The general sentiment, however, is to use reservoirs to regulate rivers (i.e., use them as aqueducts) rather than for direct supply, and - at least in England and Wales - not to use natural lakes for storage.

Reservoirs in the UK are used primarily for public water supply, the production of hydroelectric power, and the provision of “compensation water” to maintain residual stream flows at a prescribed level. Even the production of artificial spates to attract salmon into a river, distribute them upstream, and provide good flows for angling has been a feature of recent reservoir schemes. In addition to the ordinary impounding and regulating reservoirs, there are also a number of pumped-storage reservoirs in the UK, that is, basins which have water pumped from other catchments, especially by electrical power during off-peak periods.

During the latter part of the Nineteenth Century, there was a widespread establishment of upland reservoirs to provide urban water. Initially, most authorities prohibited access to the gathering grounds for sanitary reasons, and there was considerable opposition in some areas to damming natural lakes. Today, in view of advances in water treatment, as well as public demand, the tendency is to allow public access to UK reservoirs. In fact, as early as 1948 the Central Advisory Water Committee declared itself in favour of public access to gathering grounds, the Countryside Act of 1968 required water undertakings to allow public recreation on their new reservoirs as far as possible, and today the authorization for most new reservoirs includes recreational clauses dealing with fishing. Along with use for such pastimes as sailing and birdwatching, new reservoirs may now include hatcheries, tackle shops, and fish-cleaning facilities.

In the lowland reservoirs of England and Wales, put-and-take trout fisheries are the general rule. Ten of these studied by Crisp and Mann (1977) varied in size from 49 to 635 ha, and with one exception had maximum depths less than 22 m. There are also a number of upland reservoirs (over 200 m in elevation) where trout are indigenous and stocking is not believed generally useful.

5.4 Canals

Developed in the UK for commercial use at an early time, its canal era was 1760–1830, today its canals are used primarily for recreation, including fishing, although they continue to carry some freight and are important for land drainage and water supply. Some large rivers have been canalized in their lower stretches or where they pass through cities, and canals connect quite a few of the rivers (see also section 6).

Figures on the extent of the canal system vary depending upon the source and method of presentation. Thus, according to the National Environment Research Council (1972), the navigable inland waterways of England and Wales alone total 4 645 km: 2 340 km of British Waterway Board canals, and 2 305 km of other canals and rivers. The Inland Waterways Amenity Advisory Council (1975) says that with a “national network” of 1 771 km of “cruising” waterways and 966 km of “remainder” waterways a leisure canal is readily accessible to some 25 million people. The Travis Commission (1980) says that there are 4 830 km of canals in England and Wales of which 628 km are not navigable but still contain water, and that the British Waterway Board controls 2 415 km of navigable canal. The Economist (1981) says that the inland waterways of the UK as a whole total only 1 147 km. Stabler (1982) says that virtually the whole of the canal network in the UK with a total length of 3 200 km is under one national authority, the British Waterways Board. Tombleson (1982) says there are 4 800 km of canals in England and Wales. Britain (1981) says that the British Waterways Board controls 3 219 km of canal and river navigation of which only 547 km are maintained as commercial waterways or use by freight-carrying vessels. It also says that the Board maintains about 1 760 km of cruising waterways for navigation and about 1 450 km of other waterways. Worldmark (1984), Europa (1989), Pygott, O'Hara and Eaton (1990), and Britain (1990) are all in essential agreement that Great Britain has about 3 200 km of navigable waterways.

In Scotland, there are 195 km of canals according to UK/EIFAC (1979), or 298 km according to the Travis Commission (1980). Scotland's “Caledonian Canal” which connects the North Sea with the Irish Sea is 97 km of inland waterway of which 35 km is artificial canal. Opened in 1847, it runs along the Great Glen linking Moray Firth with Loch Ness, Oich, Lochy, and the sea-loch Linnhe (see Lindsay, 1968).

Whatever the correct length of the canal system in the UK, it furnishes a great deal of space for anglers (over 0.75 million adult anglers in Great Britain in 1984) especially in areas where water quality is poor, and has been instrumental in the dissemination of different species. An up-to-date discussion of the subject will be found in Pygott, O'Hara and Eaton (1990).