Minnesota conservation officials are blaming the illegal introduction of non-native ornamental or pet goldfish for large numbers of dead carp washing up on the shores of a southern Minnesota lake.

The Minnesota Department of Natural Resources said the carp died from a virus linked to koi, or goldfish. The virus also has been found in at least eight other southern Minnesota lakes in the past year.

The investigation began after dead fish began showing up on Lake Byllesby near Cannon Falls. Both the DNR and Minnesota Aquatic Invasive Research Center labs showed the fish died from infection with the koi herpes virus, which only afflicts common carp and koi.

The DNR said the virus affects the gills and skin of the fish, but cannot be transferred to humans or other animals.

Koi have been raised in East Asia for centuries and are kept by some people in aquariums and outdoor ponds. The DNR said releasing pet or ornamental fish into the wild "is illegal and can upset the balance of natural systems."

The DNR reported that the virus is being studied as a possible way to control carp, which can cause damage to aquatic ecosystems.

MPR News contributed to this report.