(COLDWATER) – State authorities say they think they know what caused several fish to be killed in a Branch County chain of lakes.

Brian Gunderman from the Michigan Department of Natural Resources Fisheries Division says that a report that was received last week made mention of fishes with sores in the Randall Lake Chain Of Lakes. Other reports that were issued never mention external symptoms on the fish.

However, Gunderman says by the time a biologist investigated the matter, the fish had been dead long enough to not give accurate lab analysis and results. He says with the warmer water temperatures in the summer, along with fungi and bacteria settling on fish after they are dead, it causes problems with lab testing.

Gunderman says the symptoms on the fish seem to be consistent with a very common bacterial disease known as columnaris, and there are several breakouts in the Branch County area each spring and summer. He says it happens most often when fish are stressed and their immune systems are not at full strength.

Gunderman says there isn’t a treatment for columnaris in a wild setting, and the kill in the chain of lakes has affected bluegill, yellow perch, largemouth bass and northern pike.

Columnaris is not a threat to humans.