Lake Erie has long been known for pollution, shifting from the industrial waste of the mid-20th century to the visible green slime of modern times. While the narrative of the lake being “dead” in the 1960s was exaggerated, it reflected the severe industrial and sewage contamination present. Significant binational efforts in the 1970s led to a substantial recovery, yet today the lake faces a complex, recurring water quality crisis. The current problems stem from contemporary nutrient runoff, which causes the most visible signs of “dirtiness,” and persistent toxic substances buried deep within the lakebed. The lake’s unique physical characteristics amplify the impact of both current and historical pollution, making it particularly vulnerable among the Great Lakes.
The Dominance of Nutrient Pollution
The most apparent cause of Lake Erie’s current poor water quality is the massive overgrowth of algae, a phenomenon driven almost entirely by excessive phosphorus loading. Its overabundance leads to a process called cultural eutrophication. The largest source of this phosphorus is non-point agricultural runoff, which includes fertilizers and animal manure washing off farmland into tributaries that feed the lake. This runoff can account for up to 90% of the total estimated phosphorus load in the western basin, the area where the algae problem is most severe.
Phosphorus enters the lake in two main forms: particulate phosphorus (PP) and dissolved reactive phosphorus (DRP). PP is bound to soil particles and is only about 25% bioavailable, meaning algae cannot easily consume it. The more problematic form, DRP, is 100% bioavailable and immediately consumed by algae to fuel rapid growth. While overall phosphorus loads have been reduced since the 1970s, the proportion of DRP has significantly increased, driving the severity of modern blooms.
This influx of DRP creates vast harmful algal blooms (HABs), which are dominated by cyanobacteria, or blue-green algae, such as Microcystis. These blooms produce liver toxins like microcystin, which pose a direct threat to human health and were responsible for the 2014 Toledo drinking water shut down. When these immense mats of algae eventually die, they sink to the bottom of the central basin where their decomposition consumes dissolved oxygen, creating vast hypoxic areas. These low-oxygen zones suffocate aquatic life and can cover thousands of square kilometers of the lakebed.
The Lake’s Unique Physical Vulnerabilities
Lake Erie is disproportionately affected by pollution compared to the other Great Lakes due to its distinct geographical and hydrodynamic features. As the shallowest of the Great Lakes, Lake Erie has an average depth of only 62 feet, with the western basin averaging a mere 24 feet. This shallowness allows the water to warm much more quickly during the spring and summer months than the deeper lakes. The warmer water temperature promotes faster biological and chemical reactions, accelerating the growth rate of algae and enhancing nutrient cycling.
The lake also has the shortest water retention time, or flushing rate, of the five Great Lakes, at approximately 2.6 years. While this short turnover might seem beneficial for flushing out contaminants, the high volume of water entering the lake from its tributaries is already heavily nutrient-laden. The shallow nature of the western basin, where most of the phosphorus enters, ensures that these nutrients remain concentrated and readily available for algal uptake.
Furthermore, the Lake Erie watershed is one of the most densely populated and intensely farmed areas in the Great Lakes basin. Approximately 12 million people live within the watershed, and the surrounding land is characterized by extensive agriculture and urbanization. This combination of high population density and heavy land use ensures a constant, substantial flow of nutrients and contaminants into the lake, which is then quickly metabolized in the water’s warm, shallow environment.
Legacy Industrial Contamination in Sediments
Beyond the contemporary problem of algal blooms, Lake Erie’s “dirtiness” also stems from a dangerous historical burden of industrial pollution stored in its lakebed sediments. Decades of heavy industry along its shores resulted in the dumping of vast quantities of toxic waste before environmental regulations were enacted in the 1970s. This legacy contamination includes heavy metals like mercury and cadmium, as well as persistent organic pollutants (POPs) such as Polychlorinated Biphenyls (PCBs) and organochlorine pesticides.
These toxic compounds are not dissolved in the water column but are instead sequestered in fine-grained sediments, particularly in the deeper, quieter parts of the lake near former industrial hubs. While buried, they pose less of an immediate threat, but they remain a long-term reservoir of contamination. Events like dredging, severe storms, or even the activities of certain bottom-dwelling organisms can re-suspend these toxic sediments into the water.
Once re-suspended, these legacy contaminants can enter the aquatic food web, bioaccumulating in fish and potentially leading to consumption advisories for humans and wildlife. The presence of these buried toxic chemicals is why certain areas of the lake, like Presque Isle Bay, were designated as Great Lakes Areas of Concern. Even as the lake visibly cleans up from nutrient pollution, this hidden layer of toxic sediment remains a source of underlying ecological risk.