Changing weather, changing water – it's time to look out for harmful algal blooms

As we jump into warmer weather, it’s time to watch for harmful algal blooms in Washington lakes and rivers. While these blooms typically appear in late summer or fall, changing climate conditions and human-caused nutrient pollution make it hard to guess where and when blooms will happen. Some lakes bloom regularly, some lakes rarely have blooms, and not every bloom is toxic. The only way to know for sure if toxins are present in an algal bloom is through laboratory testing. When in doubt, keep yourself and your pets safe by avoiding water with algal blooms and pay attention to warning and closure signs. 

What are harmful algal blooms? 

Algae are simple plants and bacteria that are a natural part of lake and river ecosystems. Under certain conditions, the algae get too many nutrients and multiply too quickly, growing into an algal bloom. Blooms can indicate the ecosystem is unbalanced, and can create issues in the food web, reduce oxygen in the water, and stop sunlight from reaching underwater plants.  

While blooms aren’t great for local waterways, only some blooms have the potential to be toxic to humans, pets, and wildlife. We call these harmful algal blooms. Please see the Washington State Toxic Algae for more information about harmful algae. 

Blooms can vary in appearance based on what kind of algae are present or is in the bloom. Most harmful algal blooms are caused by cyanobacteria. Cyanobacteria is a type of microorganism that can make their food from the sun (photosynthesis). The duration of any one bloom can be short-lived, but blooms can happen throughout the year. Their toxicity can vary from day-to-day, and not all blooms are toxic to begin with. The only way to know if the bloom is toxic is with laboratory testing. That being said, there are a few common traits of harmful algal blooms to watch out for: 

  • The appearance of slimy scum, foam, or growing clumps on the water 

  • Color can vary — blue-green, reddish-brown, pea soup green 

  • Looks like a paint spill on the water 

Additionally, be aware of these possible signs that you or your pet may have been exposed to a harmful algal bloom: 

  • Skin rashes after being in the water 

  • Sudden, unexplained sickness after drinking or playing in the water 

See a bloom? Give it room  

Since harmful algal blooms can only be identified in a laboratory, it’s best to avoid going into the water with algal blooms when possible. If you suspect you or your pet have been exposed to harmful algae, rinse off with clean water and seek appropriate medical attention. 

If you spot a bloom, contact the local lake manager. This could be the county public health department, city, a homeowners association, or state park, depending on the lake or river. Because there is no statewide, comprehensive monitoring program, reporting blooms can be helpful. Check with your local municipality to see if they have more information or monitoring data on a particular lake or river.  

Difficult to predict 

There are many factors that can lead to a harmful algal bloom. Excess nutrients, like phosphorus from fertilizer, can wash into the water and contribute to blooms. Other factors, like weather conditions, water temperature, and water flow changes, can also trigger a bloom. Cyanobacteria generally do better in warmer water, which is why we tend to see more blooms as the summer heats up.

Additionally, the intense and changing weather patterns can increase algal blooms. If there is increased, sudden rainfall, more nutrients can wash from the land into water bodies. This provides the base nutrients the cyanobacteria need to grow. If this is followed by a drought, the water body can retain those extra nutrients for longer, increasing the likelihood for a bloom. Conversely, large amounts of rainfall can wash the nutrients from one water body to another, causing algal blooms in new areas. These are a few examples of ways extreme weather conditions can contribute to blooms. 

While we know what contributes to a bloom, they are still not well understood. Each waterbody has many parts that change year-to-year, making algal blooms hard to predict. These elements can even change throughout the year—a lake with normal levels of nutrients during springtime can still get an unexpected bloom during the summer due to runoff. Similarly, a lake with high levels of nutrients can avoid a bloom if certain weather conditions are not met.

There are many elements involved in the production of a harmful algal bloom to accurately predict when and where they will occur. Because of this, it’s important to pay attention to warnings from local officials and look for the posted signs when recreating in or near water. 

What you can do to help 

While the precise triggers of each harmful algal bloom are hard to pinpoint, there are still steps you can take to keep water clean.

  • Clean up pet waste - This helps reduce nutrients and bacteria from washing into water bodies. 

  • Maintain your septic system to prevent leaks - Septic system leaks can add nutrients and  bacteria to water bodies undetected. 

  • Do not feed waterfowl, like ducks and geese - Their excess waste increase nutrient levels. 

  • Reduce or eliminate the use of fertilizers – Some fertilizers contain phosphorus, and easily wash from lawns and greenspaces into the water. 

  • Wash vehicles away from water or storm drains - The best place to wash your car is at a car wash! 

  • Maintain native vegetation around water - The plants will help filter out excess nutrients before they reach the water. 

Only time will tell if this will be a big year for algal blooms. If you want to learn more see our related links at the top of the page.