In late June, thousands of common carp died in Lake Elysian in Waseca County. The Minnesota Department of Natural Resources working with the University of Minnesota have concluded that these were caused by goldfish. It's believed that a virus was introduced to Minnesota waters by the release of or escape of ornamental koi or pet goldfish. Both the koi and goldfish are actually a type of carp. The koi has been specially bred for its colors and is used as an ornamental fish. The virus has been identified as the herpesvirus or KHV, according to the press release from the DNR.

This is now the first documented case of the virus in a wild fish population in Minnesota. It was first documented in 1996 in the United Kingdom. Carp fishing is a big sport over there. The virus has since been documented in other parts of the world but not in the wild waters of Minnesota until now.

Goldfish can typically be carriers of this virus but usually don't show signs of having it.

DNR fisheries pathology lab supervisor Ling Shen said the virus can be present in a lake without causing a fish kill, at least not until the right conditions prevail.

The lesson to be learned from this is that it's illegal to release ornamental fish such as koi or goldfish into the wild. There could be consequences in regards to the native fish population.