Conservationist David Bellamy is among a host of well-known figures backing the battle to save the wild brown trout.
The health of the brown trout, Britain's only native trout species, is considered a key indicator of the health of the country's rivers and lakes.
But the Wild Trout Trust says the fish is under threat on many fronts.
Yesterday the charity announced the appointment of several celebrity supporters for the cause.
Author and conservationists Brian Clarke becomes its president, while Dr Bellamy is one of several vice-presidents, who include broadcaster Jeremy Paxman, former-Welsh rugby star Gareth Edwards and former Liberal Democrat leader Lord Steel. Naturalist writers Jon Beer, Oliver Edwards and Peter O'Reilly also become vice-presidents.
Dr Bellamy, of Bedburn, County Durham, said: "I am delighted to have the opportunity to work with the experts safeguarding this truly wonderful fish and its habitat."
Unlike many freshwater species, the brown trout needs clean gravel in which to spawn, and cool, unpolluted, well-oxygenated water in which to thrive.
Heavy industry was once considered its main enemy, but the trust believes the fish is under pressure "by stealth".
Insecticides, herbicides and fertilisers used in intensive farming seep into waterways, killing the plant and insect life on which the trout depends, and producing growths of choking algae.
In addition, rainwater run-off, which carries sediments into rivers, clogs gravel and suffocates the eggs.
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