CHICAGO -- Asian carp, the big, hungry fish that the authorities here have for years been desperately trying to keep away from the Great Lakes, appear to have moved closer than ever to Lake Michigan. The carp, a non-native species that some fear could destroy the ecosystem of Lake Michigan by consuming what the lake's native fish eat, have long been making their way up the Mississippi River, and since at least 2002 have been the focus of an enormous effort to prevent them from reaching the lake here.

But on Friday, officials from the Army Corps of Engineers reported that genetic material from the carp had been found for the first time in a nearby river beyond an elaborate barrier system, which has cost millions of dollars and was meant to block their passage. That, officials said, means that the fish could be within several miles of Lake Michigan -- and with only one lock, regularly opened for boats, between them and the Great Lakes. No one seems certain how the carp could have found their way through the complicated barrier, which is not unlike a really powerful underwater electric fence.

And in truth, federal and state officials said, no actual carp have been spotted. But most authorities said the genetic material was a likely sign that at least a few are present.

"This is absolutely an emergency," said Joel Brammeier, acting president of the Alliance for the Great Lakes, who said that recreational boating on the lakes could also be severely damaged if the carp arrived. (Elsewhere, Mr. Brammeier said, the silvery fish, which can grow to 100 pounds, sometimes leap, hitting boaters.)

"If Asian carp get into Lake Michigan, there is no stopping them," he said, "and the volumes of water and geography make containment impossible in terms of the other Great Lakes. Control is impossible."