Barge operators struggled to keep traffic flowing steadily on the drought-lowered Mississippi River as a proposal to divert water there from the Great Lakes met opposition.

But there was good news from Ohio: Low water levels are killing off mosquitoes.Independence Day traffic on the Mississippi was steady, with two groundings reported in the Memphis, Tenn., area, Coast Guard spokesman Dave Schuster said Monday.

"They're losing hundreds of thousands of dollars each day. I guess they figure they've got to go no matter what," he said of towboat operators who can move fewer barges because of shallow spots caused by the drought.

Dredging closed the river near Greenville, Miss., and north of Memphis, Schuster said.

In Wisconsin, Gov. Tommy G. Thompson has threatened to ask the U.S. Supreme Court to halt proposals for increased diversion of Lake Michigan water to replenish the shrinking Mississippi.

An aide said the governor fears temporary diversion through Chicago and down the Illinois River in response to the current drought might become a permanent practice. He said the move is also a feint to get more water to disperse river waste in the Chicago area.

Thompson had received reports the Army Corps of Engineers might quadruple the diversion at Chicago in the next few days to fight the low-water conditions troubling Mississippi River barge tows, said James Klauser, secretary of the Department of Administration.

"The navigation of (ewage) down the Chicago River is the only navigation issue here," he said. "It's solely a matter of flushing Chicago."

In Louisiana, environmental officials said they would monitor the Mississippi more closely for salt and toxic substances as the drought continues to decrease the freshwater flow.

Levels of toxic substances still are low, but the environmental agency will increase monthly sampling to weekly, a spokeswoman said.