Summer 2021 Conservationist

Harmful Algae Blooms

by Dan Grigas, Natural Resources


To say that algae play a role in life under the water is an understatement. Algae are paramount importance to aquatic life. They provide the basis of the food web and oxygenate water and the atmosphere. Without algae, our waterways would be barren wastelands providing little in the way of biological diversity.

There are many types of algae, but algae in freshwater ecosystems fall into three main groups: diatoms, green algae and blue-green algae. Diatoms are sensitive to environmental change, so their presence lets ecologists know an ecosystem is fairly healthy (even though to the naked eye masses of diatoms can look like brown slime). Green algae are brighter; in water they can look like lime-colored strands of hair. Both diatoms and green algae are common, but as summer progresses and the weather warms, in nutrient-rich waters exposed to long stretches of hot and sunny weather, single-cell blue-green algae can also develop.

Blue-green algae, or “cyanobacteria,” form large colonies, or “blooms” that can look like dense mats, foam or floating paint, although affected waters can also look normal on the surface. Some people call these blooms “pond scum.” Blooms can be beneficial for the ecosystem, but they can also be problematic under the right conditions. When certain toxin-producing cyanobacteria dominate a bloom and start to release those toxins as the algae cells begin to die, the bloom becomes a “harmful” algae bloom, or HAB.

In animals (which of course includes people), contact with HABs can cause a range of adverse health conditions from skin irritations to liver, gastrointestinal or nervous system issues, mostly through two primary routes of exposure. The first route is direct contact with contaminated water. Swimming isn’t allowed in DuPage forest preserves, but people can still come in contact with blooms while fishing or boating, the biggest risk coming from handling wet equipment. The second route, and most prevalent for domestic pets, is ingestion. (A third but less prevalent route occurs when people inhale airborne toxins, but that normally occurs during high-speed water sports, near decorative fountains, or during extreme wave conditions, which cause fine water droplets to drift through the air, all unlikely in DuPage forest preserves.)

Because harmful algae blooms are a possibility in DuPage forest preserves, the Forest Preserve District monitors waters through summer and early fall for signs of HABs. When a potential harmful algae bloom is spotted, staff conducts an on-site test of the water. If a test is positive, the District notifies the Illinois Department of Natural Resources and the Illinois Environmental Protection Agency, posts signs at the site, and alerts future visitors via posts on the Forest Preserve District’s website and social media pages. Staff will check the site weekly until tests come back negative but will also keep an eye on the site as the season progresses in case it needs to be tested again.

So how can ecologists prevent HABs? One way is to reduce the amount of nutrients that make their way into a body of water. Adding native aquatic plants to a shoreline can create a buffer zone that absorbs nitrogen, phosphorus and other elements found in fertilizer-rich runoff before they reach the water. Other solutions include installing diffused aeration systems or treating an affected area with alum, but these options are not appropriate for all locations.

Private land owners can help fight HABs by reducing the use of garden and lawn fertilizers, which can eventually reach natural waterways via rain water runoff.

As the weather warms, harmful algae blooms will be a possibility in some DuPage waters, but by monitoring lakes and ponds and investigating mediation techniques, the Forest Preserve District will continue it efforts to get the word out when they happen.


How can I tell if water contains an HAB?

HABs can look like mats, foam or floating paint, but affected waters can also look normal on the surface, so it’s not always easy to spot them.

What should I do if I come in contact with one?

Harmful algae blooms can affect anyone, although children, seniors and people with compromised immune systems are at greatest risk. It’s best to avoid water either suspected or confirmed to have an active algae bloom. It you do get wet, wash with soap and water as soon as you can.

Make sure, too, that pets do not enter or drink any water. If a pet is exposed, wash the animal as soon as possible, and contact your veterinarian to see if you should take further action.

Are fish safe to eat during an HAB?

Some studies say yes, but others advise people to avoid eating fish during an active bloom, which is always the safest best. The biggest risk is coming in contact with an active bloom while handing tackle and any caught fish. When in doubt, pick another fishing spot.