Hundreds of fish have been discovered floating dead in the lake at Forest Lake over the past few weeks, creating a smelly environment described as “disgusting”.

Pest Fishing Adventures co-founder Nicole Whysall said she went to the lake on Sunday and found hundreds of dead fish.

“It was disgusting,” Miss Whysall said.

“I have never seen a fish killed this big or this amount of fish.”

Ms Whysall said a majority of the dead fish was the pest species tilapia, but she also saw a dead catfish, which are normally hardy as it is a native species.

Councillor Charles Strunk (Forest Lake) said about 700 kilograms of dead fish have been removed between when the council was first notified, on around July 30, to Wednesday.

On Thursday morning, Cr Strunk saw a further 35 dead fish floating on the lake.

“They [the council] did a number of tests on water quality with regard to the algae, the oxygen levels and a few other tests to make sure the environment wasn't killing the fish, such as poison,” he said.

“They have decided that what has happened is that the temparature of the lake got low enough the tilapia couldn’t survive.”

Cr Strunk said the council would be sending someone to the lake daily to monitor the situation and collect the dead fish.

A council spokesman said the council believed some pest fish species had been susceptible to temperature, but there was an ongoing investigation into algae in the lake.