Lake Michigan's water levels have plunged in recent months as the nation continues to experience record drought conditions, creating a scenario that could allow the Chicago River to flow backward into the lake.

The Army Corps of Engineers, which manages a set of locks between the lake and the Chicago River, typically keeps the lake's water level 6 inches higher than the river, but the ongoing drought has caused the lake's level to dip to its lowest point since 1964. Yesterday, the lake was just less than half an inch below the river.

Because of the dip, some people have raised concerns that the river water, which can contain up to 80 percent treated water, will empty into relatively pristine Lake Michigan, which provides drinking water to the Chicago area. But Army Corps officials say there's no reason to panic yet.

"Compared to the amount of water diverted at Chicago and compared to the amount of water at Lake Michigan, you're talking a thimbleful," said Roy Deda, deputy district engineer for project management at the Army Corps.

Water levels could continue dropping through the winter, but they are expected to rise in the coming months with spring rains and snowfall runoff. Another dry summer, however, could cause the lake level to dip again.

If the low lake level persists, the Army Corps will try to minimize backflow by creating a set schedule for opening the locks, instead of opening them on an as-needed basis.

"What we don't want to do is have significant amounts of canal water going into Lake Michigan because it's not as clean as Lake Michigan," said Gary Meden, the Army Corps Rock Island district deputy for programs and project management.

A scheduled lock system would have the greatest effect on tour boats near the city of Chicago and on commercial boats heading into and out of the lake. T.J. O'Brien, the lock that gets the most commercial use, sees about 7,500 barges pass through it each year.

Del Wilkins, an executive at Canal Barge Co. and president of Illinois Marine Towing, said opening the locks every hour would have a minimal effect on businesses. But if the water levels forced the Army Corps to open the locks only every few days -- a move proposed a few years ago in an attempt to manage invasive Asian carp populations -- the companies using the waterways would have a greater problem.

Still, scheduling the opening of the locks is not a rarity. The locks ran on a scheduled basis as recently as October, when winds lowered lake levels.

Eventually, the Army Corps and Metropolitan Water Reclamation District of Greater Chicago, which is responsible for the waterways, will try to find a way to minimize backflow without affecting the locks, perhaps by pumping lake water -- instead of river water -- into the locks.

Engineers have managed the lake's and river's water levels since 1900, when a series of canal locks were built to force the river to flow away from the lakes. Prior to the reversal, the river had been slow-flowing -- sometimes flowing in different directions -- and sewage and other pollution built up in the area, creating a public health issue. Although water in the river is now treated, its historical stigma persists.