Freshwater algae
People and animals can become seriously ill, or even die, after exposure to toxic algae (cyanobacteria) also called harmful algae bloooms. Although not all blooms are toxic, toxicity is hard to predict and can only be detected by laboratory tests.
We help with toxic algae in several ways. We are starting a rule to set limits for how much toxic algae is considered pollution. We fund a testing program for lake managers and residents to test if their freshwater algae samples are toxic. Also, we help advise local municipalities and health departments who manage lakes and administer a permit to control aquatic plants and algae.
For information or concerns about a current algae bloom or if the water is safe to swim please contact your local health department.
Why is algae a problem?
Many types of algae are natural, helpful, and important for producing oxygen and food. However certain conditions can cause algae to multiply too quickly, resulting in algal blooms. This often happens in warm, slow-moving water that has excess nutrients that help the algae grow.
In addition, some types of algae produce toxins that can harm people, wildlife, and pets. These algae go by several names: blue-green algae or cyanobacteria, but when there is too much of it, we call it harmful algae blooms or (HAB). These harmful algae blooms are hard to predict, because they do not always produce toxins. Also, it can change quickly, a bloom that tests non-toxic one day can become toxic the next.
The toxins can cause many different health effects that range from a mild skin rash to serious illness or in rare circumstances, death. Learn more about the effects of harmful algae blooms from the Environmental Protection Agency (EPA) webpage or the Washington State Department of Health webpage.
We are beginning the process to set limits on cyanotoxins
We are developing limits for certain toxins (called cyanotoxins) that are produced by cyanobacteria during harmful algae blooms. We set these limits in our water quality standards through a rulemaking process. The goal of this rulemaking is to help protect people’s health while swimming or doing other recreational activities in lakes and rivers.
The limits, also called criteria, describe the quality of water needed to support a specific use or goal of a water body. For example, some water bodies are used by salmon for habitat and reproducing or some lakes are used for drinking water. These are called designated uses. In this rulemaking, we are protecting the designated use of contact recreation, that is activities where you are likely to touch the water, such as swimming, fishing, or boating.
How would Ecology use these new criteria?
These criteria can help us better identify water bodies that need a cleanup plan to address the pollution that causes harmful algal blooms. A water cleanup plan is a science based approach to reducing pollution. It describes actions needed to reduce pollution so that it meets state standards. For example, a water cleanup plan could describe the steps Ecology and others are required to take to reduce cyanotoxin levels in a lake so that people could safely swim without health concerns.
How are we setting the limit for cyanotoxins?
When we develop criteria for recreation, we want to protect everyone, including the most vulnerable people. Vulnerable people include those that are just naturally sensitive to low amounts of toxins (in other words, they might get sick but someone else might not after swimming in the same lake for the same amount of time). It also includes people who unintentionally drink a lot of lake or river water.
For this rulemaking, the most vulnerable people are young children, who might be swimming in fresh water for a few hours a day and accidentally drink the water. Based on data, we calculated that it could be possible for someone to accidentally drink about 12 ounces of water while swimming (that is about equal to the amount in a soda can) . We also think about the quality of the data and what sort of studies are available. We consider the differences, for example, between a health study looking at a large, diverse human population compared to a small animal study. We then take this information and calculate cyanotoxin values that, when met, will allow all people to safely enjoy recreating.
Learn more
We will be sharing our preliminary thoughts about our approach to setting limits at our webinar. During the webinar, you can ask us questions and get more information. We also invite you to send us your questions through a brief survey. Visit our rulemaking webpage to learn more.
Join us for an information webinar
This webinar is offered via Zoom:
Wednesday, Sept. 30, 2026, at 2 p.m.
Register for the webinar
This is not the only opportunity for input. We will hold a formal public comment period with public hearings on the draft rulemaking in early 2027.
Take our survey
Take two minutes to tell us your questions about this project, and let us know if you have ideas of how to better reach you with this information.
Related links
Contact information
Jeff Zenk
Water Quality Communications Manager
jeff.zenk@ecy.wa.gov
360-791-3177