By Greg Farnham
A widespread die-off of common carp began the later part of July in the upper reaches of the Rock River at the Horicon Marsh and Lake Sinissippi in Dodge County, Wisconsin.
Wisconsin DNR have evaluated water conditions and did not discover any factor of temperature, dissolved oxygen, etc., that might have caused the die-off. Bacterial or viral infection was suspected.
Samples of fish carcasses were evaluated by the DNR and sent to the U.S. Fish and Wildlife Service-Fish Health Center in La Crosse, Wisconsin. The test results were positive for Koi herpes virus, which is specific for members of the Cyprinidae family including the common carp. Other fish species do not appear to be affected.
Last week, the carp kill reached the river stretch at Watertown, Wisconsin, and just a few days ago large numbers of dead carp were reported in Fort Atkinson in Jefferson County. So, in four weeks or so, the virus has remained virulent and spread downstream about 100 miles. Soon, it will likely affect carp in Lake Koshkonong and presumably continue to move downstream.
According to DNR information, the virus will likely continue to spread down river until water temperatures become cooler. So, depending on air temperatures going forward, the virus may reach Illinois in the next week or so.
We’ve attached for your information two DNR news releases about the die-off and Koi herpes disease. Also attached is an information brochure regarding safe methods of disposal of dead animals. We’ve advised folks to remove the fish carcasses from their shoreline and dispose of them by burial, composting, incineration or rendering. Always wear gloves when handling the dead fish since secondary bacterial infections are common.
Should a fish die-off occur in your area, depending on the number of fish involve,d the aesthetics can be a bit unpleasant for a while. However, the infected fish normally die in 24 to 48 hours, and the effects will pass as the carcasses decompose and disintegrate. We on Lake Sinissippi are no longer seeing evidence of the kill, and the lake (river) condition has returned to normal.
Please distribute this information to other officials and interested persons in your area.
Greg Farnham is a coordinator of the Rock River Trail Initiative and commissioner of the Lake Sinissippi (Wisconsin) Improvement District.