Biologists with the Illinois Department of Natural Resources are following up on this head scratcher: why have thousands of Asian carp turned belly-up on the Illinois River?

Some biologists are welcoming the Asian carp die-off, blaming the silverhead and bighead carp for crowding out tasty sport fish.

The Illinois DNR’s Mike Conlin says the deaths are a mystery, but a virus might be behind them. Asian carp are susceptible to a virus called spring viremia. Problem is, other Illinois fish are susceptible, too.

“We don’t know if it will affect any of those species in the future or not, if it is the spring viremia of carp. We do know that we have it in Illinois waters. It was found in the Cal-Sag channel three years ago,” he said.

Conlin says federal scientists gathered carp tissue and expect results within a few weeks. In the meantime, Conlin says deaths have tapered off, and there’s no evidence the fish kill has spread beyond the Illinois River.