Understanding Algae

Don't really get what's going on with blue-green algae in Lake Erie? Read on for an overview of what the problem is and what causes it. 

What’s the problem?

Nutrient pollution that finds its way into Lake Erie is contributing to a big problem: harmful and nuisance algal blooms. Sometimes blooms are small and localized, but other times vast mats of algae that span hundred or even thousands of kilometers may form. Large algal blooms are becoming more common in Lake Erie.

Nuisance algae

Nuisance algal blooms do not necessarily pose a significant risk to human or environmental health, but they may impede our enjoyment and use of the lake--for example, by clogging pipes of drinking water intakes, discoloring water and leaving a foul mess on beaches and fishing gear. They also diminish wildlife habitat and can make waterfowl sick.


Harmful algae

Some algal blooms are harmful to people and the environment. For example, algae use up oxygen in the water when they decay, leaving less for fish and other plants. In some cases, large numbers of fish and aquatic plants may die for lack of oxygen. And sometimes, algae may even produce toxins that are lethal to fish, pets and wildlife. If this toxic algae is ingested by humans, they could get sick, or, in rare cases, even die.

When has it happened?

In the late summer and early fall of 2017, an algae bloom in the Western part of Lake Erie was so large it covered an area of over 1,800km2. That bloom wasn’t toxic, but it hurt local industries like fishing and tourism. Just three years earlier, in 2014, another large algal bloom in the lake was so toxic that the city of Toledo, OH announced a drinking water ban for its 500,000 residents. In 2011, the largest recorded algal bloom on record hit the lake, but that record was broken in 2015, when an even larger bloom occurred.   

What causes it?


The introduction of nutrients--such as phosphorus and nitrogen--into the lakes, rivers and streams that feed into Lake Erie is a leading cause of algal blooms. Phosphorus is the big driver behind the harmful algae blooms in the western end of Lake Erie, with runoff pollution from farm fields being the biggest source. In the 1960s and 1970s, the majority of nutrients in Lake Erie were from “point sources”-- that means, sources that directly release pollution into the lake, such as sewage plants. Today, about 85% of nutrients entering Lake Erie come from “non-point sources.” This means pollution that reaches the lake because rainwater (or snowmelt) picks up contaminants on the ground and washes them into Lake Erie or its tributaries (streams and rivers that run into the lake).

Farming and fertilizers


Fertilizers from agriculture are a big cause of non-point source pollution entering Lake Erie. Farmers use fertilizers to help their crops grow. But when it rains, fertilizers can get washed away from where they were first applied and end up in the lake. This is called “runoff pollution.” If fertilizers help crops to grow, they also help algae to grow. About three-quarters of the land around Lake Erie on the Canadian side is farmland. That translates to a lot of fertilizer application that happens around the lake. A recent report by the International Joint Commission estimated that some 58 million tonnes of phosphorus is used in the Lake Erie basin each year. It is this phosphorus that is of most concern and driving the growth of harmful algal blooms.

Physical characteristics of Lake Erie

Lake Erie also has some physical characteristics that make it more vulnerable to the impacts of pollution. It is much shallower than the other Great Lakes and has less volume of water. Therefore, there is less water to dilute runoff pollution than the other lakes. being shallow, Lake Erie is also the warmest of the Great Lakes, and blue-green algae prefer warmer water.












Another factor that can lead to more severe algal blooms is land-use change around the lake, in particular a decrease in forests and wetlands. Forests and wetlands help to absorb runoff and reduce the total volume that reaches the lake. However, natural areas have been replaced with farms, as well as residential and commercial developments, which means less trees and wetlands to absorb excess water and nutrients.

Climate change

Algal blooms tend to be the largest and most severe during years when we’ve had a very wet spring (March-June) --that is, years when there is lots of rainfall and/or snowmelt during this period. All that precipitation means more runoff pollution enters the lake. Climate change is already changing precipitation patterns in the Great Lakes area. More precipitation--in particular rainfall--and more intense rainfall events will mean more runoff entering Lake Erie, and therefore more nutrients in the water.  


Blue-green algae is caused by human activity—and we have the power to stop it too! Take action by donating to the Lake Erie Challenge today.