Lake Superior receding, warming

Deep enough to hold the combined water of all the other Great Lakes and with a surface area as large as South Carolina, Lake Superior’s size has lent it an aura of invulnerability.

But the mighty Superior is losing water and getting warmer, worrying scientists, those who live near its shores and companies that rely on the lake.

The changes to the lake could be signs of climate change, although scientists aren’t sure.

Superior’s level is at its lowest in 80 years and will set a record this fall if, as expected, it dips three more inches. Meanwhile, the average water temperature has surged 4.5 degrees since 1979, significantly above the 2.7-degree rise in the region’s air temperature in the same period.

That’s no small deal for a freshwater lake that was created from glacial melt as the ice age ended and that remains chilly in all seasons.

A weather buoy on the western side recently recorded 75 degrees, “as warm a surface temperature as we’ve ever seen in this lake,” said Jay Austin, assistant professor at the University of Minnesota Duluth’s Large Lakes Observatory.

Water levels of the other Great Lakes also have receded since the late 1990s. But the suddenness and severity of Superior’s changes worry many in the region. Shorelines are dozens of yards wider than before, exposing mucky bottomlands and rotting vegetation.

On a recent day, Dan Arsenault of Sault Ste. Marie in Michigan’s Upper Peninsula watched his two daughters play in mud on the southeastern coast where a few years ago the water was waist deep. A flotation rope that had designated the swimming area rests on moist ground. “This is the lowest I’ve ever seen it,” Arsenault said.

Superior still has a lot of water. Its average depth is 483 feet, and it reaches 1,332 feet at the deepest point. Erie, the most shallow Great Lake, averages 62 feet and is 210 feet at its deepest.

Yet along Superior’s shores, boats can’t reach mooring sites and marina operators are begging the U.S. Army Corps of Engineers to dredge shallow harbors. Ferry service between Grand Portage, Minn., and Isle Royale National Park was scaled back because one of the boats couldn’t dock.

Sally Zabelka has turned away boaters wanting to dock at Chippewa Landing marina in the eastern Upper Peninsula, where not long ago 27-foot vessels easily made their way up the channel from the lake’s Brimley Bay. “In essence, our dock is useless this year,” she said.

Another worry: As the bay heats up, the perch, walleye and smallmouth bass that have lured anglers to Zabelka’s campground and tackle shop are migrating to cooler waters.

Low water has cost the shipping industry millions of dollars. Vessels are carrying lighter loads of iron ore and coal to avoid running aground in shallow channels.

In a Grand Marais pub, retiree Ted Sietsema voiced a suspicion not uncommon in the villages along Superior’s southern shoreline: The government is diverting the water to places with more people and political influence -- along Lakes Huron and Michigan and even the Sun Belt, via the Mississippi River.

“Don’t give me that global warming stuff,” Sietsema said. “That water is going west. That big aquifer out there is empty but they can still water the desert. It’s got to be coming from somewhere.”

That theory doesn’t hold water, said Scott Thieme, hydraulics and hydrology chief with the Corps of Engineers district office in Detroit. Water does exit Lake Superior through locks, power plants and gates on the St. Marys River, but in amounts strictly regulated under a 1909 pact with Canada.

Austin said he was concerned about the effects the warmer water could have. “It’s just not clear what the ultimate result will be as we turn the knob up,” the Minnesota-Duluth professor said. “It could be great for fisheries or fisheries could crash.”