The river has been invaded by the American signal crayfish which is affecting the native protected white-clawed crayfish.

It supports a wide range of fish, and its upper reaches are the only location in Sussex where native white clawed crayfish can be found.

It held good populations of native crayfish until at least the 1980s.

The result has been the gradual eradication of native crayfish from the UK's rivers.

They inhabit burrows and are aggressive, apparently outcompeting native crayfish.

Until recent times, native crayfish and many freshwater fish species inhabited the river.

Isolated streams are the last refuge of the native British white-clawed crayfish.

In 1959, to bolster dwindling stocks of native crayfish, the signal crayfish was introduced to Sweden.

After 150 years of contact, no resistance has been discovered in native European crayfish.

A keen environmentalist has been ordered to pay £4,000 after catching, cooking and eating endangered native crayfish.