ENVIRONMENT Agency officials have been braving freezing weather to help rid a South Lakeland tarn of an alien species of fish, writes Countryside Reporter Ruth Lythe.

Rather Heath Tarn, near Staveley, is to be intentionally poisoned by Environment Agency officers to kill topmouth gudgeon which have invaded its waters.

The fish originally come from Asia and grow to only nine centimetres in length, but they mature and breed very quickly, prey on the fry and eggs of native fish species, compete for food and habitat and spread disease and parasites. The munching marauders are believed to have arrived mingled with an import of fish from Eastern Europe and pose such a threat that it is illegal to hold, keep or release them, without a licence.

On Monday, EA officers began the work of removing large native fish including tench, bream and roach from Rather Heath Tarn.

"There are two phases to this operation, the first is to remove the native coarse fish, using large nets, 100 metres in length and four metres in depth," explained EA fisheries stock officer Matt Brazier.

This is the first time that such a method of tackling a topmouth gudgeon invasion has been used by the Environment Agency although so far everything is going to plan.

"So far we have been very successful and have managed to remove hundreds of carp and bream," said Mr Brazier.

The fish are kept in special keep nets and then scooped out of the water by helpers on to a sorting table, where they are identified and taken for a break to an EA fish farm at Chorley.

Next, a special kind of fish poison called Piscicide Rotenone will be added to the waters. This will kill the fish but not harm any other wildlife in the area of the tarn.

The task is expected to continue into April although, if the weather is poor, it could take longer because weather conditions must be good before the poison is applied so that water levels can be monitored.

"It is impossible to say exactly how many of the topmouth gudgeon are in the tarn but we did a survey and there are certainly tens of thousands of them," said Mr Brazier.

Members of the Windermere and Ambleside District Anglers Association, which issues permits for the tarn, were also on stand-by to help out with the removal of the native fish.

"We are very satisfied with what the Environment Agency is doing, from the respect that they have looked closely at all the other options before going ahead with this," said WDAA member Patrick Arnold.