There has been one bighead carp in particular in the Lake Calumet region. As recently as last week, apparently there were 14 additional hits of the environmental DNA. That has been the primary means, if you will, of an early warning that they have gotten beyond it. A couple have been found in ponds in the Chicago area, but the only way they could have gotten there was by human transport. I think there's only been one actual fish found.
On June 18th, 2012. See this statement in context.