The results are not conclusive evidence that the fish are living and breeding in the St. Croix -- none has been found in the river -- or that they are absent from the Mississippi, DNR officials said. The DNA could have come from dead carp, live carp someone dumped in the river or fish pellets used in hatcheries.

Still, it ratchets up the fear considerably, they said.

"This is disappointing news," said DNR Commissioner Tom Landwehr.