MORE than 50 dead Redfin were retrieved and about another 10 sighted in an as-yet unexplained fish kill at the Ess Lagoon last weekend.

The fish, ranging in size from less than 10 centimetres long to around 30 centimetres, were found scattered right around the banks of the lagoon after being spotted by a resident on a morning walk.

However, visitors in the adjacent camping area told the Casterton News they had noticed several dead fish in the lagoon, as early as last Saturday.

Casterton Angling Society Secretary and Friends of the Glenelg River member, Brian Murrell, attended the lagoon after being told of the deaths and collected 52 fish – all Redfin - from around the banks.

Mr Murrell said in his lifetime of fishing at the popular local spot, he had not seen anything like the weekend’s event, but did not believe it was a great cause for alarm.

“I haven’t seen them in this number, not like this, but you see the odd dead one here and there,” he said.

“I think these have been dead for a couple of days, the way they smell and there’s been something feeding on them, quite a few have got the eyes picked out.

“But there’s fish activity in the water here this morning, there’s no fish lying near the top of the water or the banks, gasping for air, so I think whatever happened is over and they’ve recovered.

“And I don’t think it’s a major water issue, the parrots are drinking the water, the swans are still here all healthy and happy, there’s other birds still active on the water.”

Mr Murrell said is his opinion, while the deaths could be attributed to a number of factors – including a disease found in Redfin and not lethal to native fish species – an oxygen depletion in the Ess Lagoon water was the most likely explanation.

“It’s unusual that it’s only Redfin that seems to be affected,” he said.

“If there was trout in here – and we’re only assuming there’s still trout, from the last time they were put in – then they’d be the first to be affected by a lack of oxygen.

“But there’s activity in the water this morning, no yabbies crawling out looking for air, or tortoises and the episode with the Redfin seems to have passed, we’d have to assume there’s no trout left here right now.

“A lack of oxygen seems most likely, with all the duck weed and the Elodea (weed) … it breaks down and sinks to the bottom and reduces the oxygen in the water … there’s been a lot lately.”

No health alerts have been issued for the Ess Lagoon and the Glenelg Hopkins Catchment Management Authority, responsible for the Glenelg River and its associated waterways, including the lagoon, is investigating the fish kill.

“It was reported to the CMA on Monday that a number of Redfin were dying in Ess Lagoon at Casterton,” the authority’s waterways executive manager, Chris Solum said.

“The CMA has reported the fish death event to the (Environment Protection Authority) and will monitor the situation.

“The cause of the event is not yet known.”