Illustration by Daniel Hertzberg

Editor's note: Lake Erie's problems are among the concerns faced by scientists and politicians at meetings for Great Lakes Week October 11-14.

On a cloudy morning in early August, Peter Bichier steers a 26-foot motorboat from an Ohio marina toward the Canadian border. The waters of Lake Erie are nearly transparent here, a reminder of why this southernmost of the Great Lakes supports a multi-billion-dollar fishing and vacation industry. But as the research vessel turns west toward the Michigan shoreline, the water grows murky, clogged with a toxic blue-green algae called microcystis that, on sunnier days, forms a stinky scum on the lake’s surface.

Bichier, a research technician at the University of Toledo’s Lake Erie Center, dangles a long, white plankton net off the side of the boat, then hauls it in and filters the sludgy water into a canister for testing back in the lab. "Dogs get sick when they drink this," he says: three in Ohio died last year after swimming in a contaminated inland lake not far from here, and nine people got sick (including one with memory loss and partial blindness) after skin contact.

After a decades-long absence, blue-green algae is again flourishing in Lake Erie -- and it’s never been worse than it is this summer. The algal infestation is just one of many factors that biologists in Ohio, Michigan, and elsewhere say are pointing toward an ecosystem in danger of collapse.

The lake’s center contains a growing dead zone, devoid of oxygen during summer months. Invasive species such as zebra and quagga mussels are wreaking havoc with its ecology. The fish that make Lake Erie a tourism draw, including yellow perch and smallmouth bass, are seeing their predators grow and their habitats shrink. Ducks, loons, and mergansers that feed on lake fish have died in recent summers from botulism poisoning. Swimmers in some areas have been advised this year not to swallow the water.

What would it mean to lose one of our Great Lakes? The environmental and economic calamity could devastate the region’s tourism, sport fishing industry, drinking water supply, and wildlife, and could also take a toll on human health. And there would be plenty of blame to go around, from changing agricultural methods to inattentive politicians to weaknesses in our nation’s bedrock environmental protections -- many of which can partially trace their existence to concern over Lake Erie in the first place.

Erie is the most fertile of the Great Lakes: It contains only 2 percent of their water but 50 percent of their fish. Its biological abundance, and its location in a densely settled corner of the Midwest, make the prospect of collapse all the more frightening. If conditions grow worse, imploding native fish populations could decimate Lake Erie’s recreational fishing industry. (Fishing generates $7 billion a year throughout the Great Lakes.) The water supply for 11 million people could become undrinkable without expensive treatment. And blue-green algae, linked to liver cancer in China and fatal poisonings in Brazil, could pose a grave threat to people here, too, particularly if ingested.

"If we don’t turn this around, someone whose health is already compromised -- a very young person, a very old person, someone less tolerant of the toxin -- is likely to die," says aquatic biologist Jeffrey Reutter, director of Ohio Sea Grant and Ohio State University’s Stone Laboratory in Lake Erie.

The lake itself nearly died once before. In 1969, Time magazine practically wrote its obituary, describing how "each day, Detroit, Cleveland and 120 other municipalities fill Erie with 1.5 billion gallons of inadequately treated wastes, including nitrates and phosphates. These chemicals act as fertilizer for growths of algae that suck oxygen from the lower depths and rise to the surface as odoriferous green scum." Between human sewage and pollution from steel, paper, and automobile plants, Time said, Lake Erie was "in danger of dying by suffocation."

John Hartig remembers riding his bicycle down to the Detroit River, which flows into Lake Erie, to fish -- and seeing its water turned black and purple from industrial waste. Now a biologist who manages the Detroit River International Wildlife Refuge, Hartig also watched as the oil-fouled Rouge River, which eventually empties into Lake Erie, caught fire in 1969, sending flames 50 feet into the air. (He chronicled the disaster in his 2010 book Burning Rivers.) "I saw the smoke from my house," he says. "You don’t get that image out of your brain."

Back then, Americans responded -- not just to "what they were seeing, but also to what they were smelling," says Hartig. "There were front-end loaders taking algae off the bathing beaches and dead fish. The lake had gone anaerobic. That means no oxygen. That means the smell of rotten eggs." Those scenes, and the fires on Cleveland’s Cuyahoga River, which empties into Lake Erie, provoked an outcry that helped trigger some of the great advances of the early 1970s: the first Earth Day, the Environmental Protection Agency, the Endangered Species Act -- and the Clean Water Act, which (along with a U.S.-Canadian agreement) forced wastewater-treatment plants to sharply reduce the phosphorus they were dumping into Lake Erie. Coupled with bans on phosphate laundry detergents (which supplied up to 50 percent of the phosphorus in sewage), those reforms led to a two-thirds reduction in the main nutrient feeding the lake’s harmful algae.

Without phosphorus, the organisms couldn’t bloom, die, and deplete oxygen from the lake as they decomposed (creating a condition called hypoxia). Moreover, restrictions on mercury, DDT, and other toxins helped bring back fish such as walleye, a popular local dish, and birds such as the bald eagle. "We literally went from being the poster child for pollution problems to the Walleye Capital of the World," Reutter says.

Beginning in the mid-1990s, though, harmful algae and the dead zone began reappearing. The problem has accelerated steadily over the past decade. The magnitude of this year’s problem became evident two weeks ago, when Thomas Bridgeman, an aquatic ecologist at Toledo’s Lake Erie Center, notified his colleagues that there was twice as much microcystis in the water this summer as last. It was the largest crop since the center began measuring the algae in 2002 and considerably greater than the next-largest year, 2009.

In late August, Ohio state officials posted signs on two Lake Erie beaches, Kelleys Island and Maumee Bay State Park, warning swimmers not to swallow the water and to avoid algae scum. Fishermen were distributing photos showing water the color of pesto. And in an August 29 NASA satellite photo, the lake’s westernmost portion looked as though it were covered entirely by a garish green cloud.

"We are now at the levels of algal blooms and hypoxia that we were at in the 1970s," says Bridgeman. "We’re back to the bad old days."

And this time, with clean-water regulations and programs already under attack and a whole new set of scientific challenges, the problem could be much harder to fix.

Deadly Intruders

As big as the forces arrayed against Erie’s recovery are, some of the modern culprits driving it back toward collapse are the size of a fingernail.

In the late 1980s, oceangoing ships accidentally discharged zebra and quagga mussels into the Great Lakes. The mussels, which come from river deltas around Europe’s Black and Caspian Seas, hitchhiked in the water those ships draw into their "ballast" tanks at port to provide stability. Once the ballast water and the mussels were dumped in Lake Erie, they colonized its bottom and fundamentally altered its ecology. In essence, they teamed up with another invasive species, the round goby, a fish from the same region that feeds on the mussels.

The gobies not only outcompete other small bottom dwellers; they also prey on smallmouth bass, a favorite Lake Erie sport fish. "We’ve been scuba diving out in the lake," says Tyler Lawson, a biologist at Stone Laboratory. "The bottom is literally crawling with these round gobies. We’ve seen at times 20 gobies sitting in a circle around a smallmouth-bass nest, just waiting to rush in to eat all those eggs."

The mussels weren’t around in the 1960s, the last time the lake nearly choked on algae, but they’ve proven to be important players in its return and in the growth of the lake’s hypoxic dead zone. Zebras and quaggas are efficient feeders; they consume algae so thoroughly that they initially make the water clearer. But they’re also picky eaters: As they feast on "good algae" that forms the base of Lake Erie’s food chain, they reject toxic blue-green algae like microcystis. This gives microcystis an advantage by removing its competitors. Clear water also helps sunlight penetrate the lake’s surface, which in turn stimulates more algal growth. Finally, the mussels excrete phosphorus in a form algae can easily consume. You could hardly design a more deadly toxic-algae-creating machine.

The algae at the surface, in turn, plays its part to make the lake’s depths more toxic. When microcystis dies and sinks in the lake’s waters, the decomposition process sucks up oxygen. This is a special problem in Erie’s Central Basin, where the lake is exactly the wrong depth. It’s deep enough to form a colder, self-contained bottom layer in the summer -- so much colder, in fact, that it doesn’t mix with the upper layer. It’s as if an invisible barrier separates them. But that bottom layer is so shallow that it contains limited oxygen. If rotting algae uses all the oxygen, it creates a perfect breeding ground for botulism toxin, which the mussels and gobies transfer efficiently up the food chain when they are preyed on by larger animals.