Lake Erie supports the economies of two nations and provides drinking water for approximately 12 million people. Its warmer, shallower waters make it the most biologically productive of the Great Lakes, fueling a billion-dollar recreational fishing industry. Despite its value, the lake faces persistent pollution challenges. While historical industrial pollution and sewage releases have largely been mitigated since the 1960s, the current primary threat is nutrient loading from non-point sources. This degradation of water quality threatens public health and the economic viability of the Lake Erie basin.
The Dominant Pollution Issue: Harmful Algal Blooms
The dominant pollution issue is the annual outbreak of harmful algal blooms (HABs), particularly in the shallow Western Basin. These massive blooms are primarily composed of cyanobacteria, often called blue-green algae, with Microcystis being the most common species. Cyanobacteria produce potent toxins, notably microcystin, a hepatotoxin that can damage the liver.
The severity of this threat was illustrated during the 2014 Toledo water crisis, where microcystin was detected in the city’s finished drinking water. This event led to a two-day “do not drink” advisory for nearly 500,000 residents. Beyond the immediate health risk, the decomposition of these large blooms consumes vast amounts of dissolved oxygen. This process leads to seasonal hypoxia, or “dead zones,” most notably in the Central Basin, where oxygen levels drop below the 2 milligrams per liter threshold.
These hypoxic zones can cover up to 1.5 million hectares and begin to form as early as July. When oxygen is depleted, aquatic life is stressed, and fish kills can occur, disrupting the lake’s ecosystem. While microcystin is the most common toxin, researchers have also identified saxitoxins, a group of powerful neurotoxins produced by other cyanobacteria like Dolichospermum.
Tracing the Sources of Contaminants
The resurgence of harmful algal blooms is driven by an excess of nutrients, specifically phosphorus, from non-point sources. The Maumee River watershed, the largest tributary to Lake Erie, contributes nearly half of the total phosphorus load to the Western Basin. The most troubling development is the increase in Dissolved Reactive Phosphorus (DRP), which readily fuels algal growth.
DRP loads from the Maumee River have increased by over 200% since the mid-1990s, returning to levels seen in the 1970s. Agricultural runoff is the main driver, with inorganic fertilizers contributing a majority of the DRP load during the critical March-to-July spring period. Certain conservation practices, such as no-till farming, can unintentionally increase DRP loss through surface runoff despite reducing soil erosion.
Lake Erie also contends with legacy contaminants that persist in the sediment. Industrial chemicals like Polychlorinated Biphenyls (PCBs) and heavy metals such as mercury and lead remain concentrated in the Western and southern Central Basins. Although PCB sediment concentrations have declined since the 1970s, they still exceed probable effects guidelines, necessitating ongoing fish consumption advisories due to bioaccumulation.
The lake also faces an increasing threat from Contaminants of Emerging Concern (CECs), including microplastics and pharmaceutical residues. Lake Erie holds one of the highest concentrations of microplastics in the world, estimated to be over four metric tons floating in the lake. These plastic particles are joined by pharmaceutical and personal care product residue that current wastewater treatment plants are not designed to remove.
Current Monitoring and Restoration Strategies
The United States and Canada established a binational agreement to address the excessive nutrient loading. The primary goal is a 40% reduction in the spring load of total phosphorus and dissolved reactive phosphorus entering the Western and Central Basins from 2008 levels. Specifically, the total phosphorus load to the Central Basin must be reduced from 10,000 metric tons to a target of 6,000 metric tons annually.
Achieving this reduction relies heavily on the widespread adoption of agricultural Best Management Practices (BMPs) in the major watersheds. Farmers are encouraged to use practices like the 4R Nutrient Stewardship approach, which focuses on applying the right source, rate, time, and place. Additional BMPs include planting cover crops, establishing vegetative filter strips along waterways, and implementing variable-rate fertilization technology.
To manage the immediate public health risk, agencies utilize sophisticated monitoring and early warning systems. The National Oceanic and Atmospheric Administration (NOAA) produces a daily Harmful Algal Bloom forecast using satellite imagery and hydrodynamic models to predict the location and movement of the algae. Scientists also deploy advanced instruments, such as Environmental Sample Processors, which provide near-real-time data on microcystin toxin levels. This monitoring allows water treatment managers to prepare for toxic blooms and issue timely public warnings.