Chalk Rivers, The State of Englands Chalk Rivers

Chalk river wildlife

Protection

Ten chalk rivers are designated as river Sites of Special Scientific Interest (SSSIs) for their wildlife interest. Of these, the Rivers Lambourn, Itchen, Wensum and Hampshire Avon are also of European importance and are candidate Special Areas of Conservation (cSACs) under the Habitats Directive.

Plants

The water plants growing in most chalk rivers are characterised by water-crowfoot, water-starwort and lesser water-parsnip. These dominate in spring and early summer. As summer progresses, watercress and water forget-me-not encroach from the margins.

To grow healthily, water-crowfoot needs clean, swift-flowing water and silt-free gravels. It became less common in the dry years of the mid-1990s. However, in the last five years river flows have increased, and it is now coming back on many rivers.

The spread of non-native invasive plants such as Japanese knotweed, giant hogweed and Himalayan balsam is an increasing threat to native bankside plants. Local attempts to eradicate them have had little success.

Invertebrates

In high-quality chalk rivers, there is a great diversity of aquatic invertebrates, with a wide range of insects such as caddisflies, mayflies, and stoneflies.

Over the past few years, anglers have become increasingly concerned about declining fly life, citing low summer flows, high winter flows, silt and water quality problems.

The southern damselfly is one of Europes most endangered insects. It can still be found in old water-meadow ditches and shallow channels, notably in the Test and Itchen valleys.

The white-clawed crayfish used to be extremely common in most chalk rivers. They have declined to very low levels in recent years, and have been virtually lost from many rivers, including the Hampshire Avon, Dorset Frome and the Kennet. The main reason for the decline is a fungal disease which is carried and transmitted by American signal crayfish which was introduced into the UK in the mid-1970s.


(c) Natural Image, Bob Gibbons
Flowering water-crowfoot, Ranunculus spp.

(c) Dr Cyril Bennet
Ephemera danica, the classic chalk river mayfly

White-clawed crayfish, Austropotamobius pallipes


(c) Natural Image, Bob Gibbons
River Frome at Bradford Peverell

Fish

Chalk rivers support a variety of fish species. These include brown trout, salmon, grayling, bullhead and lamprey. Numbers of salmon in southern chalk rivers declined in the late 1980s and have stayed at very low levels.

Much of todays fly-fishing on chalk rivers is dependent on stocked trout. Stocking too many trout in a river may affect populations of wild trout and alter the balance of the fish community.

Figure 2 Return of adult salmon to three chalk rivers, 1988-2001

Estimated from electronic fish counters
Source: Environment Agency, Centre for Ecology and Hydrology


(c) Nick Giles
Brown trout

Catch and release helps maintain salmon stocks
Figure 3 Otters in chalk river catchments

Source: Environment Agency


Road deaths are now the highest non-natural cause of otter mortality

Mammals

Chalk rivers are important for water voles and otters. Otters are recovering well from the brink of a pollution-related extinction in the 1970s. However, water voles have declined dramatically in the UK. Despite strongholds on some chalk rivers, they remain vulnerable to attack from escaped American mink.

Birds

Wetlands - such as wet woodlands, flower-rich fens and wet grasslands - depend on a supply of clean water from springs, and on high water levels. They once occurred widely alongside chalk rivers. Birds such as lapwing, redshank and snipe need these wetlands for nesting and feeding. As wetlands have disappeared, often due to drainage, these birds have been lost from their traditional breeding areas.


(c) Dennis Bright
Chalk rivers historically supported healthy breeding populations of lapwing


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