Recreational water users urged to be vigilant about harmful algal blooms

With summer approaching and recreation on the state’s waterways set to increase, the State Water Resources Control Board asks the public to be mindful of freshwater harmful algal blooms in rivers, lakes and reservoirs, as they can cause illness and are especially harmful to children and pets.

Last year, the water boards received 240 reports of these blooms across the state. To learn how to stay safe, respond or report a bloom, and track multiple blooms statewide, visit its website.

Most harmful algal blooms are formed by cyanobacteria, small microbes that live in nearly every habitat on land and in the water. Increased water temperatures, slow moving water, and excessive nutrients cause cyanobacteria to rapidly multiply and form these harmful blooms.

It is important to distinguish cyanobacteria from other algae and non-toxic water plants that are not thought to pose hazards to health. Harmful blooms can be a variety of colors such as green, white, red or brown and may look like thick paint floating on the water. Not all will appear on the water’s surface; some form mats at the bottom of a waterbody, and others float at various depths.

Cyanobacteria are capable of producing toxins that have the potential to harm the environment, people, pets, wildlife or livestock. Dogs and children are most likely to be affected because of their smaller body size, increased potential to swallow water while swimming and tendency to stay in the water longer.

Recreational exposure to cyanobacteria and associated toxins can cause eye irritation, skin rash, mouth ulcers, vomiting, diarrhea and cold and flu-like symptoms.

Pets can be susceptible because they tend to drink while in the water and lick their fur afterward, increasing their risk of exposure and illness. Symptoms with animals include vomiting or diarrhea, lethargy, abnormal liver function test results, difficulty breathing, foaming at the mouth, muscle twitching and sometimes death. More information about health impacts for domestic animals and livestock can be found on the portal’s Domestic Animals webpage.

The California Water Boards recommend that people practice healthy water habits while enjoying the outdoors this summer at your local lake, river or stream:

  • Heed all instructions on posted advisories if present.
  • Avoid algae and scum in the water and on the shore.
  • Keep an eye on children and pets. If you think a harmful algal bloom is present, do not let pets and other animals go into or drink the water or eat scum/algal accumulations on the shore.
  • Don’t drink the water or use it for cooking.
  • Wash yourself, your family and your pets with clean water after water play.
  • If you catch fish, throw away guts and clean fillets with tap water or bottled water before cooking.
  • Avoid eating shellfish if you think a harmful algal bloom is present.

Get medical treatment immediately if you think that you, your pet or livestock has gotten sick after going in the water. Be sure to alert the medical professional to the possible contact with cyanobacteria. Also, make sure to contact the local county public health department.

To report a bloom, do one of the following: Fill out the Bloom Report form on the portal — email:; call the HABs hotline at (844) 729-6466 (toll free); or contact your County Public Health Office/

For more information about HABs, visit: California Harmful Algal Blooms Portal: California Cyanobacteria and Harmful Algal Bloom Network: California Department of Public Health.