Massachusetts wildlife officials believe they know why hundreds of dead fish were found in a Wales lake this weekend.

Richard Hartley, a biologist with the Department of Fisheries and Wildlife, said that warmer-then-normal water temperatures in Lake George due the recent heat wave contributed to the death of many white perch.

“In this case, it’s what we call and epizootic. It’s an organism – likely a bacteria, a virus –  that’s commonly present in the lakes and ponds in Massachusetts, but as water temperatures increase, their numbers go up dramatically,” Hartely said Monday. “And, generally, a single species or a family of fish is targeted and that’s what you see.”

Hartley said this is the second year in a row white perch in Lake George have died off – for the same reason. And it’s not unusual. Hartley said between a dozen and three-dozen fish kills are reported to the state each. He said most are due to natural causes.