The Sweetwater Seas Under Siege - Part 3: Toxic Tide: How Microscopic Mussels and Farm Fertilizer Killed Lake Erie’s Recovery
The first ecological catastrophes in the Great Lakes focused on managing the top of the food web. The government poisoned the parasitic sea lamprey. Biologists then introduced Pacific salmon to control the alewife population. However, the latest wave of biological destruction attacks the system from its most crucial and vulnerable point: the bottom. This third invasion is far more difficult to fix. It arrived in the form of noxious cargo carried by overseas freighters.
Overseas vessels pick up ballast water at foreign ports to stabilize their loads. When these ships arrive in the Great Lakes, they discharge up to 10 Olympic swimming pools’ worth of water (about 2.5 million liters). This released water carries millions, or even billions, of organisms. These ships function like syringes, injecting biological pollution that cannot be fixed by plugging a pipe or capping a smokestack. This pollution is alive and aggressively breeds.
The Mussels Storm the Front Door
The deadliest invaders among the Great Lakes’ 186 nonnative species are the zebra and quagga mussels. These two closely related mollusks are native to the Black and Caspian Seas. Their arrival was predicted and ignored for decades. As early as 1921, a natural history curator warned that introduction of the zebra mussel was highly probable. In 1964, a biologist cautioned that Dreissena polymorpha (the zebra mussel) would likely become established in North America. Crucially, a 1981 study specifically mentioned zebra mussels as a primary threat lurking in the ballast tanks of Seaway freighters. The U.S. and Canadian governments took no action based on this information.
In 1988, a student discovered the first zebra mussel in North America in Lake St. Clair. Lake St. Clair is a 24-mile-wide (38.6 km) body of water connecting Lake Huron to Lake Erie. News of the novel “zebra clam” quickly spread. Within a year, zebra mussels were smothering the bottom of southern Lake Michigan near Chicago. This was a 600-mile (966 km) range expansion achieved, once again, by hitchhiking on freighters.
The zebra mussel proved to be an engineering nightmare. Unlike native Great Lakes mussels, the zebra mussel excretes a plaque from a gland, creating remarkably tough, leathery threads called “byssal” tethers. An adult mussel can spin over 500 of these threads to create a cement-like bond to hard surfaces. Within months, Coast Guard buoys hauled from Lake Erie were unrecognizable, coated completely in shells. By December 1989, a massive infestation caused the water supply for 50,000 residents in Monroe, Michigan, to shut down for over two days when mussels and ice plugged a three-foot-diameter intake pipe [120–121].
The Quagga Takeover
An even more ominous development occurred in 1989 on Lake Erie. Researchers discovered a slightly different version of the zebra mussel, later identified as the quagga mussel. The quagga is named after a subspecies of actual zebras that went extinct in the 1800s. While zebra mussels were the initial problem, quagga mussels eventually proved to be far more devastating.
Quagga mussels can thrive in the deep, cold, dark lakebed, unlike zebra mussels. By 2005, the quagga mussel population completely flipped the invasive ratio in Lake Michigan. Quaggas comprised 97.7 percent of the invasive mussel population. If Lake Michigan were drained today, it would be possible to walk almost the entire 100 miles (161 km) between Wisconsin and Michigan on a solid bed of trillions upon trillions of quagga mussels. The chaos brought by this takeover is profound.
Of invasive mussel population in Lake Michigan comprised by quagga mussels by 2005
Collapse at the Base of the Food Web
The quagga mussel destruction is so immense that it is hard to fathom. The mussels act as filter feeders, consuming plankton from the water. Plankton forms the essential foundation of the Great Lakes food web. In Lake Michigan, the plankton-stripping power of the mussels caused a massive increase in water clarity.
Biologists measure water clarity using a Secchi disk. Before the mussel invasion in the late 1980s, Lake Michigan’s average Secchi depth was about 20 feet (6 meters). By 2010, the average clarity had tripled. Readings began coming in at depths beyond 100 feet (30.5 m). This nearly vodka-clear water is not a sign of a healthy lake. It is evidence that the bottom of the food web is collapsing.
The devastating effects quickly traveled up the food chain. Lake Huron suffered a catastrophic Chinook salmon demise. The crash corresponded directly to a drop in the salmon’s preferred prey, the alewife. That alewife drop, in turn, was tied to a 90 percent plummet in phytoplankton. Fishery managers discovered the exotic food web built by Howard Tanner in the 1960s was dangerously fragile.
Plummet in phytoplankton levels due to mussel filtering
Native fish suffered similarly. Whitefish are built to grub for food on the lake bottom. Before the mussels arrived, a seven-year-old whitefish weighed nearly five pounds (2.3 kg). By 2003, it weighed barely a pound (0.45 kg) because its favored shrimp-like organism had vanished. The famished whitefish then began eating the sharp-shelled mussels whole. Their internal orifices stretched to the diameter of a pinky from excreting the paste of crushed shells.
On the shoreline, the mussels also created conditions for massive nuisance seaweed blooms. A seaweed-like plant called Cladophora needs three things to thrive: sunlight, a hard surface, and nutrients. Mussels provide all three. Their shells offer a perfect surface. Their filtering allows sunlight to penetrate deeper. Finally, their phosphorus-rich excrement fuels the plant’s growth. This endless, brilliantly green, hair-like forest later breaks off, washing ashore to rot. This septic-smelling muck now plagues spectacular shorelines across the lakes.
Lake Erie’s Recovery is Overwhelmed
The mussel invasion fundamentally altered Lake Erie, magnifying a pre-existing pollution problem. Lake Erie was once dubbed “North America’s Dead Sea” in the late 1960s due to massive algae blooms. This crisis was caused by overwhelming levels of phosphorus, primarily from sewage and laundry detergents. Following the landmark Clean Water Act of 1972, billions of dollars were spent upgrading sewage treatment plants and slashing detergent phosphorus. The recovery was successful. The lake returned to being the “Walleye Capital of the World”.
Today, however, Lake Erie faces a new, complex threat. The mussels have rewired the lake’s system, and it no longer responds to nutrients the same way. Crucially, the mussels are just smart enough to know the taste of toxic algae. Laboratory videos show a zebra mussel sucking in a toxic algae fleck called microcystis and immediately spitting it out with vigor. The mussels decimate the edible, non-toxic algae populations through constant, selective filtering. This leaves a lake increasingly dominated by the toxic strains that the mussels avoid.
Meanwhile, farmers across the Maumee River basin, which feeds Western Lake Erie, struggled with their own pollution controls. The basin sprawls across over four million acres (1.62 million hectares), three million of which is cropland (1.21 million hectares). Farmers have increasingly turned to no-till growing practices to prevent soil erosion. However, this leaves factory-made fertilizer pebbles sitting exposed on top of the fields.
If heavy rains hit before the fertilizer is absorbed into the crops, the nutrients wash away in a highly potent dissolved state. Biologists compare this dissolved phosphorus to “gasoline,” noting it is absorbed by algae within 60 seconds. The older form, particulate phosphorus, acted more like a hunk of coal on a campfire. Compounding the problem, big early spring rains have become more common in the western Lake Erie basin.
This shift means the total volume of nutrient flowing into Western Lake Erie able to fuel algae growth is now higher than it was during the 1970s. The amount of dissolved phosphorus has increased by at least 150 percent since the mid-1990s. This potent runoff, combined with the mussels’ selective filtering, creates blooms that are now far more dangerous.
Increase in dissolved phosphorus levels since the mid-1990s
The Water Supply Shutdown
The result is a return of massive algae blooms, which have become fixed to the rhythm of the seasons. In 2011, a satellite tracked a poisonous, green-as-paint slick covering nearly 2,000 square miles (5,180 km²) of Lake Erie. This was more than three times larger than the previous record bloom.
The threat escalated quickly. In 2013, toxic microcystis blooms overwhelmed a public water treatment plant for a community of 2,000 residents east of Toledo [225, 237–238]. The outbreak forced a temporary shutdown of the public water system [237–238]. This was the first time toxic algae had completely overwhelmed a Great Lakes public treatment plant.
The true crisis struck in the summer of 2014. National Oceanic and Atmospheric Administration (NOAA) scientists were monitoring a budding microcystis bloom near the Maumee River mouth. Winds drove the toxic plume directly into Toledo’s main water intake pipe. Routine sampling at 6:30 p.m. on Friday, August 1, confirmed the toxin had breached the system. It exceeded the World Health Organization’s (WHO) recommended threshold of 1 part per billion.
Toledo Mayor Michael Collins issued a late-night “DO NOT DRINK THE WATER” order for 500,000 residents. Officials also issued the alarming warning: DO NOT BOIL THE WATER. Boiling would not destroy the toxins but would instead increase their concentration. Panic immediately set in. Within hours, every store that was open had run out of bottled water. National Guard units rushed to the city with pallets of water and pre-mixed baby formula.
The water department got the problem under control more than two days later. Mayor Collins used the crisis to warn other Great Lakes mayors. He called the Toledo shutdown the “canary in the coal mine”. The event proved the reliability and sustainability of safe drinking water was fundamentally threatened.
The Regulatory Abyss
The core problem, according to Mayor Collins, was not the weather. It was the agricultural runoff. The Clean Water Act, passed following the 1969 Cuyahoga fire, successfully targeted industrial and municipal pollution from “point sources” (pipes). However, farm runoff is classified as “nonpoint” pollution and was left largely untouched by the law. This deficiency of governance has allowed the nutrient pollution to return with devastating effect.
Scientists estimate they need a 40 percent reduction in spring phosphorus runoffs into the Maumee River watershed. This reduction could slash the toxic blooms by at least 90 percent. However, farmers believe their individual practices are sufficient to protect local water quality. They view themselves as better stewards than their ancestors. Nonetheless, the lake is telling a different story.
Reduction in phosphorus runoffs needed to slash toxic blooms by 90%
The Toledo crisis pushed politicians into action. Michigan, Ohio, and Ontario agreed to work toward a 40 percent reduction in phosphorus discharges. Ohio also banned spreading manure on frozen ground and required training for fertilizer application. However, the agreement did not require any new laws to force these cuts.
This new, bottom-up ecological chaos—where invisible mussels amplify invisible toxins—shows that simple solutions like stocking salmon are no longer applicable. The next step requires politicians to confront the regulatory loopholes that prevent the Great Lakes from truly healing.