By Kari Lydersen
Washington Post Staff Writer
Sunday, January 27, 2008

CHICAGO -- A decade ago, Chicago winters meant monumental ice hillocks and caves forming along the lakeshore, skirted by interlocking ice sheets like a giant jigsaw puzzle.

Today, it is rare to see more than a thin frozen shelf or a few small ice floes sloshing in Lake Michigan below the city's skyline.

Decreased ice cover on the Great Lakes, probably caused by increasing air and water temperatures and high winds, is a major culprit in lowering water levels, which have hurt the shipping industry, forced lakeside power plants to extend their cooling pipes, frustrated recreational boaters, dried up wetlands and left coastal landowners with docks extending over yards of unsightly muck.

In September, Lake Superior broke its 81-year-old low-water record by 1.6 inches, and last month it was a foot below its seasonal average. It appeared that Lake Michigan and Lake Huron would log record lows for January until storms helped levels stay above the marks set in the 1960s.

The low water has forced freighters that haul iron ore, steel, limestone and other raw materials to lighten their loads and change their routes to avoid running aground in shallow harbors and waterways.

"They literally do load these ships by the inch," said Stuart H. Theis, executive director of the U.S. Great Lakes Shipping Association. "To the lowest common denominator, the shallowest point along the way."

In the past two years, freighters have hit bottom or had to turn around in numerous locations, including Muskegon Harbor and the Saginaw River in Michigan and Rochester, N.Y.

The Lake Carriers' Association, which represents "captive" ships that travel only within the Great Lakes, has called for increased dredging at numerous "choke points" in response to low water levels. LCA spokesman Glen Nekvasil said vessels were running an average of 15 percent below capacity last season. Depending on the size of the ship, every inch of lost draft -- the depth to which a ship descends -- means 50 to 270 tons less cargo.

"And we're not talking inches, we're talking feet," Nekvasil said. "It's not just affecting the steamships; it's the steelworkers who depend on that iron ore, the workers at the limestone quarries. We move the raw materials that keep everyone else going."

Environmentalists are concerned that the drying of wetlands along the shores will have serious effects on commercial and recreational fishing.

"We firmly believe the changes we're seeing are impacting fisheries, possibly in a dramatic way," said Jeff Skelding of the National Wildlife Federation. "Disruption of habitat will impede fish species from being able to reproduce."

Marc Gaden, spokesman of the Great Lakes Fishery Commission, said the changes may be conducive to some species and harmful to others. The same can be said for people.

"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."