New data indicates that the number of invasive species in Lake Michigan continues to rise.
It also shows a drop in the amount of prey fish on which the lake's large sport fish feed.
The overall picture casts a cloud of uncertainty over the future of the lake's sport fishery.
Scientists from the US Geological Survey found lower amounts of prey fish in the lake last fall during their annual survey than anytime since 1973.
That's when the government started tracking the smaller fish eaten by salmon, lake trout, steelhead and other species coveted by anglers.
Invasive zebra and quagga mussels in the lake tripled last year while the number of bottom-dwelling goby fish increased 16-fold between 2005 and 2006.