The Environment Agency (E.A.) and local angling groups suspect poachers may be responsible for the death of around 1,500 fish on a stretch of the River Lark near Mildenhall, Suffolk.
Distressed and dead fish were spotted by a member of the public lon July 26, who called the E.A.
With the aid of members of the Lark Angling Preservation Society (L.A.P.S.) they immediately sprung into action to save any living fish by adding hydrogen peroxide to increase oxygen levels in the water and removing dead fish to prevent further pollution.
Species such as roach, bream, perch, tench, chub and pike were among the fatalities with some of the larger fish weighing as much as 1.8kg/4lbs.
Investigations as to the cause are ongoing, but both the E.A. and L.A.P.S. suspect a pesticide called Rotenone may have been added to the river by poachers.
Rotenone is sold as an organic pesticide but is also traditionally extracted from plant roots by many native peoples and used for catching fish.
When added to water, poisoned fish come to the surface and are easily caught. While potentially lethal to fish due to its rapid absorption into their bloodstream through the gills, fish caught by this method can be eaten as the chemical is poorly absorbed by the human gut.
Recent studies have however linked long term exposure to Rotenone to Parkinson's disease.
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