Recreation During Harmful Algal Blooms

Algal blooms occur most frequently in nutrient-rich waters during hot, calm weather. Many lakes and reservoirs in Utah are subject to these conditions during the summer and early fall. Toxic blooms in recreational waters can cause illness in humans and kill livestock and pets that drink the water.

The “algae” in algal blooms are actually photosynthesizing bacteria called cyanobacteria. They can cause illness in humans, pets, waterfowl, livestock, and other animals that come in contact with them.

Recreational Activities

Since it is very difficult to tell when toxins are being produced from an algal bloom, avoid recreating in or on water that has a greenish layer of scum or a floating mat. You are much more likely to experience adverse health effects if you swim, wade, waterski, jet-ski, or windsurf in or on water containing an algal bloom. Boating, however, is generally fine, as is fishing.


Children love to play in the water, but typically do not understand the health risks. They may drink the water because they are thirsty or swallow it accidentally while swimming. Children also weigh less, and so a smaller quantity of toxin may trigger an adverse effect.

Many farm ponds, golf course ponds, and stormwater detention ponds are constructed to trap nutrients, eroded soil, and other debris, preventing these materials from reaching nearby lakes, ponds, and streams. But because more nutrients may be available and because these types of ponds are generally more shallow and warm, it is possible for them to experience more frequent harmful algal blooms that may produce toxins.

If a scum layer or floating mat is present or the water looks like pea soup or green or blue paint, do not let your children or pets swim in it.


Animals are usually eager to swim in or drink lake water. They may experience skin irritation if they swim in water with an algal bloom, but they are more likely to have a severe reaction, even death, from drinking or eating cyanobacteria or licking it off their fur. Keep pets away from waters with algal blooms and any surrounding shorelines that contain accumulated algal scum.


Preliminary research shows that fish are generally safe to eat. Rinse the prepared fish in clean water prior to cooking and remove all fat, skin, and organs before cooking since toxins are more likely to collect in these tissues.


Because natural surface waters contain bacteria, algae, viruses, and other pathogens that if consumed may pose health risks, you should never drink untreated water in recreational areas. Don’t go into the water and keep children and pets away. Never drink or cook with water from an algal bloom. If you come in contact with the water, wash off thoroughly with soap and another source of water if available.

Personal water filtration devices for camping or hiking have not been proven to be effective in treating water contaminated by a harmful algal bloom. Boiling water will not remove the toxins; in fact, it will concentrate them and increase the water’s toxicity.

For more information, visit: Wisconsin Department of Natural Resources, the New York Department of Environmental Conservation, Oregon Health Authority, Washington Department of Ecology, and the U.S. Environmental Protection Agency.