Officials say the virus, koi herpes, is not harmful to humans or other fish, but could cause secondary bacterial infections that can cause illnesses in humans.
It is encouraged that people use protective clothing such as gloves when removing dead carp due to any other bacteria the fish may carry.
Fish carrying the virus may show signs of damaged gills, sunken eyes and enlarged spleens.
The DNR began investigating the die-off on July 21st in the state and federal waters of Horicon Marsh and Lake Sinissippi.
The bacteria is naturally present in surface water and when fish are stressed or their immune system is suppressed, the bacteria can cause infections and diseases.
Given the dense population of carp in the Rock River system, biologists believe the disease will continue to advance until water temperatures begin to cool as fall approaches.
Koi herpes caused significant carp die-offs in New York in 2005, Michigan in 2011 and Ontario Canada in 2007 and 2008.