Fish are still dying in the River Ouse a month after it was polluted by pesticides.

Investigations by the Environment Agency have revealed the deaths suffered by many of the bream were due to a severe and aggressive secondary infection in the water.

Stuart Taylor, the area fisheries manager, said: "The fish have been found in an appalling condition. Some are still alive with their spines protruding from their flesh.

"Aquatic animals are particularly sensitive to pesticides that have been developed to target terrestrial insects. Both fish and invertebrates may survive an initial pollution only to fall victim to a secondary infection.

"The presence of any pollutant will stress the aquatic environment and the animals that live within it.

"Like us, when stressed, these animals become more susceptible to infections around them, but they are normally kept in check by the animals' immune systems."

Water samples have confirmed the pesticide level in the water has reduced as expected, with residual levels caused by riverbed sediments.

Mr Taylor said: "It may take a couple of years before the invertebrate populations fully recover.

The public can report any environmentally damaging incidents on 0800 80 70 60.