Lack of oxygen killed 50 lake trout in Welshpool
More than 50 trout found dead in a Powys lake are believed to have suffocated due to a lack of oxygen, says the Environment Agency.
The agency launched an investigation at a private fishing pond in Welshpool last week.
Its officers have not found an external source of pollution, but believe that decomposing plants could have reduced oxygen levels in the water.
The agency had pumped oxygen into the water to help the remaining fish.
It said it had advised the lake owner on steps he could take to manage the situation.
Initial reports indicated that the pollution had turned the water, which feeds the Lledan Brook, milky in colour.