Harmful Algal Blooms

When blooms go bad

Algae are tiny, naturally occurring plants that grow in water (some bacteria are also referred to as algae). When algae populations grow extremely rapidly in a confined area or grow to the point where you do not need a microscope to see them, they are referred to as algal blooms.

Blooms can be found within most bodies of water throughout the Great Lakes region, but they thrive in shallow, warm, still bodies of water like ponds and smaller lakes. Blooms are also becoming more frequent in some parts of the Great Lakes, including Lake Michigan’s Green Bay, Lake Huron’s Saginaw Bay, and Lake Erie’s shallow western basin. Scroll to the bottom of the page for an interactive timeline of algal blooms in Lake Erie and ongoing efforts to study and eradicate them.

Most algal blooms are harmless, but certain types of algae may pose a risk to humans, animals, and water quality. Algae and algal blooms are generally not considered harmful unless they are capable of producing toxins and people come in direct contact with them.

What is a harmful algal bloom?

A harmful algal bloom (HAB) is a bloom of blue-green algae that potentially contains toxins. Blue-green algae are actually cyanobacteria that contain chlorophyll similar to true algae. They reproduce rapidly, are typically found at or near the surface of the water, and are known to produce toxins. HABs can cause fish kills, foul up nearby coastlines, and produce conditions that are dangerous to aquatic life, as well as humans.

Blooms can range in color from red to bright, neon green to more blue-green. A bloom can look like a scum, foam, or mat on top of the water or like paint that has been spilled in the water. They are also sometimes accompanied by an earthy, pungent, or musty smell. However, not all algal blooms give off an odor or affect the appearance of water, and toxins can remain present in the water even when a bloom has dissipated.

Blue-green algae that form HABs have been known to produce a wide array of neurotoxins, liver toxins, cell toxins, and skin irritants. Humans or animals that consume large amounts of these toxins may experience muscle cramps, twitching, paralysis, cardiac or respiratory difficulty, nausea, vomiting, and liver failure. Skin irritants, found in nearly all blue-green algae blooms, can produce skin irritation, rashes, and gastrointestinal distress.

The most dominant blue-green algae in the Great Lakes is Microcystis, which can produce microcystin, a liver toxin and skin irritant.

What causes HABs?

Harmful algal blooms do naturally occur in the Great Lakes but have increased since the mid-1990s (see the timeline below for a full picture of HABs in Lake Erie). Blue-green algae thrive in conditions with excess phosphorus or nitrogen, which can come from sources like malfunctioning septic systems, household or industrial detergents (though modern products now use less phosphorus), lawn fertilizers, and urban and agricultural runoff. Blooms are also more common in warm, sunny, calm waters. The blooms often persist for several weeks to a few months, depending on air and water temperature, sunlight, water flow, and naturally occurring bacteria levels.

Some scientists also link the increase of HABs to the invasion of zebra and quagga mussels in the Great Lakes. These filter-feeding mussels eat good algae and release blue-green algae back into the water intact.

How can I avoid getting sick?

When in doubt, stay out! If there are visible scums of algae in the water, it may be best to keep people and pets away.

  • Whenever you go swimming in a lake, pond, or river, always rinse yourself off.
  • Rinse off pets that have been swimming.
  • Avoid drinking water from lakes and rivers, as they may harbor algal toxins or other pathogens. Boiling the water will not get rid of algal toxins.
  • Pay attention to any warning signs posted at the beach.
  • Avoid taking boats, canoes, kayaks, jet skis, and other water crafts through algal blooms.
  • If anyone becomes ill after swimming, seek medical attention immediately. Seek veterinary assistance if a pet appears ill.
    • Signs of illness in humans include: numbness of lips, tingling in fingers and toes, dizziness, headache, rash or skin irritation, abdominal pain, diarrhea, or vomiting.
    • Signs of illness in pets include: weakness, staggering, convulsions, difficulty breathing, or vomiting.

What can I do to decrease the risk of HABs?

  • Reduce or eliminate your use of fertilizers.
  • Choose low-phosphate or phosphate-free versions of products like soap and dishwasher detergent.
  • Wash your car on the lawn so the runoff filters through the grass instead of running straight to the gutters.
  • Consider planting a rain garden or purchasing or building a rain barrel to cut down on runoff.
  • Properly maintain your septic system.
  • Consider installing a pond aeration system for small ponds and lakes that have had algae blooms in the past.

How can we keep track of HABs?

NOAA’s Great Lakes Environmental Research Lab (GLERL) produces the HAB Tracker, a Lake Erie bloom forecast available in a variety of visual and text-based formats. The forecast looks like a weather map and shows where concentrations of algae are highest. Key information on the HAB Tracker page includes a 5-day surface forecast of HABs, a vertical distribution forecast at 12 specific monitoring stations, and the latest weekly microcystin monitoring data taken at 8 monitoring stations. The page also provides a 5-day forecast of wind and waves for reference, as well as the latest usable satellite imagery of Lake Erie.

Why does Lake Erie experience HABs?

The western basin of Lake Erie has experienced harmful algal blooms for decades. The basin’s warm, shallow waters are enriched with nutrients from nearby urban and agricultural regions, providing fertile habitat for blue-green algae. Click through the timeline below to learn more about the history of HABs in Lake Erie and ongoing efforts to study and eliminate them.