Wrong kind of weather for the River Lea fish

Environment Agency aerating the Lea at Three Mills London July 2013 © EA

THOUSAND of fish have been dying in the River Lea — and the wrong kind of weather is being blamed.

The Environment Agency said that rapid pressure changes during thunderstorms reduced the water’s ability to hold enough oxygen for fish. And fish suffered when oxygen levels were low.

The Lea flows gently through Lee Valley nature park  in northeast London, but its bucolic appearance is misleading: the river is considered one of Britain’s most polluted.

The agency believed it reacted well to the disaster. Thanks to its “quick response”, oxygen levels were rising to between 20% and 25%.

The agency said: “Agency fisheries officers worked through the night of Tuesday [23 July 2013 ] and Wednesday [24 July 2013 ], aerating the Lea at Three Mills on the Lower River Lea.” Mechanically aerating the water had helped to raise oxygen levels that “crashed as a result of recent thunderstorms”.

© david.altheer@gmail.com
Environment Agency picture, top, shows aeration under way at Three Mills, Bow, above

The aeration helped to create “a refuge area” for bream, perch, pike and roach. The Canal and River Trust, which  works with the agency, had also been aerating along the river.

The agency added: “We will continue the aeration at Three Mills lock until after the weekend and levels have improved.”

“In some cases fisheries officers have carried out hydrogen peroxide-dosing to increase oxygen levels in the water.

“With thunderstorms forecast in some parts of the country over the next few days, a sudden change in weather could adversely affect fish stocks and fisheries.”

Fisheries officers had walked the river, removing the dead fish. The agency said: “We have had no further reports of dead fish along the Lea Navigation.”

Thames21, an organisation set up to improve London’s watercourses, was critical of the agency’s explanation of what caused thousands of fish to die.

Theo Thomas, Thames21 senior programme manager, said: “The trigger was the influx of a large amount of polluted rainwater, washed off roads across East London. The hot weather played a factor, lowering the dissolved oxygen levels. The pollution that enters the Lea on a daily basis lowered them further.”

The pollution washed off the roads increased bacterial activity, using up the oxygen. The rain did not itself cause the thousands of fish deaths. Raindrops aerate water.

Thomas added: “Rain washed off dry summer roads will be full off pollutants and warmer than the river it enters — perfect for bacteria.”

David Altheer 270713

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