Great Lakes' Lower Water Levels Propel a Cascade of Hardships

"Whether [low lake levels] are a good or bad thing depends on how you use the Great Lakes," said Cameron Davis, executive director of the Alliance for the Great Lakes. "It's a problem for commercial shippers, recreational boaters, fishery managers. For people who love the beach it's probably a good thing."

Great Lakes levels have historically fluctuated, with relatively high levels in the 1980s and early 1990s. Scientists say Great Lakes levels are on an overall downward trend, which is likely to continue as a result of reduced ice cover, increased evaporation, and warmer air and water temperatures.

"Since the late 1970s, we've seen a slight decline in precipitation and a steeper increase in evaporation," said Cynthia E. Sellinger, a hydrologist with the National Oceanic and Atmospheric Administration. "We've been in a different climactic regime for the last decade with higher air temperatures, which means more evaporation."

Great Lakes scientists and engineers have also suggested that low water levels in Lake Michigan and Huron could be caused by the "bathtub drain" created by dredging in the St. Clair River, which connects Lake Huron to Lake St. Clair and ultimately to Lake Erie. Dredging and subsequent erosion have caused the water to flow faster out of the upper Great Lakes and eventually out the St. Lawrence Seaway. Michigan legislators have called for the installation of concrete barriers on the river bottom to stanch its flow.

Some scientists have also blamed a geologic effect known as isostatic rebound, referring to the gradual rising of Earth's crust since the weight of the glaciers has been removed. This effect could essentially be pushing water out of the lakes at an accelerated rate, though some scientists say the effect is probably minute compared with other factors.

More than 99 percent of the Great Lakes' water is left over from melting glaciers, and less than 1 percent is replenished each year through groundwater, rainfall and snowmelt. Water lost through increased evaporation or diversion may be gone forever.

A legislative package known as the Great Lakes Compact would prohibit almost all diversions outside the Great Lakes basin. The legislation, already passed by Illinois and Michigan, must be ratified by all eight Great Lakes states and Congress to take effect.

"We don't know the extent to which each factor is causing the lower lake levels, so we should take steps to minimize the effects where we can," said Environment Illinois advocate Max Muller. "That means passing the Great Lakes Compact and stopping global warming."