Piles of dead fish were seen on the banks of the lake during last week’s heatwave, with several lake users blaming low oxygen levels in the shallow, heated water.

Lake Learmonth Advisory Committee chairman Fon Ryan said the lake was 68cm deep at its deepest point, while the mud flats at its margins were steadily increasing.

“Especially in the warm weather and low water levels, low oxygen events can affect them,” he said.

Victoria’s fish stocking program has seen rainbow trout released into Lake Learmonth in recent years, after a healthy wet season replenished the water levels of the lake over the summer of 2010-11.

Mr Ryan said the return to dry conditions was concerning for the recreational use of the lake.

Last summer it was declared too shallow for motor sports and now angling was also in jeopardy, he said.

“It’s only going to go lower unless there’s a large rainfall event, which isn’t on the horizon,” Mr Ryan said.

He said without significant rainfall, the lake would drop to 50cm at its deepest point by autumn.

Learmonth resident Rolf Wojciechowski said he was alarmed to find a dozen dead rainbow trout piled up at the edge of the lake last Friday, during the fifth consecutive day of extreme hot weather.

He said they were all rainbow trout between 30-40cm long.

The Courier nature writer Roger Thomas said trout did not survive well in shallower, warmer waters due to oxygen depletion.

“It’s presumably the hot weather combined with the shallow nature of Lake Learmonth at the moment,” he said.

rachel.afflick@fairfaxmedia.com.au