The Chief Sanitary Inspectorate is running a series of epidemiological tests in the waters of the Zegrze Reservoir, near Warsaw, after dead fish were discovered.

The health authorities have closed down designated bathing areas in both the reservoir and the Bug river, which flows into it, on Friday, following widespread death of hundreds of fish, triggered by low oxygen levels in the waters.

No bacteriological or chemical contamination has been detected, nor any symptoms pointing to pollution of water intakes.

Experts have begun oxygenating the Zegrze Reservoir by means of special diffusers, aimed at preventing the fish from suffocating. These devices have never been employed over such a vast area, as they are usually used for oxygenating fish-breeding ponds, and water treatment plants, said Ivetta Biały, from the Provincial Office of Mazovia.

Last week, experts disagree as to what is causing the death of thousands of fish in rivers in eastern Poland.

Recent days have seen vast numbers of dead fish floating on the surface of rivers in eastern Poland, including the Bug, Wieprz and Liwiec. Anglers consider the situation an environmental disaster, claiming that bringing the fish stock back to previous levels will take years. 

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Fishy riddle in eastern Poland, thenews.pl, July 7