Rivers

Whilst otters are targeted as an indicator species of river health, not all species are faring so well. Water voles and crayfish are two notable exceptions.

Dorset's extensive chalk downland creates a unique chalk river habitat
 
Nationally water voles are in decline, although the 2002 survey suggested that several counties in this region including Dorset are starting to recover. The decline is due to a number of reasons including habitat degradation and increased predation by the American mink.
Improving water vole numbers along with improving otter numbers may indicate that we making progress in tackling some of the issues with our waterways.

View water vole distribution maps.

Surveys are conducted on a 5 year basis and contribute to the Biodiversity Action Plan.

White-clawed crayfish are found in parts of Dorset, but nationwide they are being displaced by their American cousins. These are farmed and seem to carry a disease that only kills the white-clawed.

Find out more about the Otters and Rivers Project.

Introduced species such as the American mink and an American crayfish that upset our natural flora.
Introduced plants can also be a problem as they can smother river banks and potentially outcompete the native species that constitute a good habitat.