Make room for algal blooms

Spring marks the start of algae season in Washington’s lakes and rivers. While harmful algal blooms (also known as cyanobacteria) are more common in late summer and fall, shifting climate patterns and nutrient pollution make them hard to predict. These algal blooms have the potential to disrupt freshwater ecosystems and produce toxins that are harmful for human and animal health.

However, not all algal blooms are harmful, and the only reliable way to detect toxins is through laboratory testing. To keep yourself and your pets safe, avoid water with visible algae and follow all posted warnings and closures.

What are harmful algal blooms?

Algae and cyanobacteria occur naturally in water but can become a problem when they grow rapidly, forming what's known as a “bloom.” This often happens in warm, slow-moving water rich in nutrients.

Cyanobacteria/blue-green algae are often confused with green algae. However, unlike cyanobacteria, green algae generally do not produce toxins.

Not all toxic blooms are visible

Harmful algae can grow in different parts of a water body. While a harmful algal bloom is often found suspended or floating throughout the water column (planktonic zone), some harmful algae attach to the bottom of a water body (benthic zone) and form algal mats. Toxic algal mats are trickier to spot - the water can appear clear even when toxins are present. Mats can grow on bedrock, vegetation, sand, and other plants attached to the bottom of a water body.

 

What causes an algal bloom?

There are several contributing factors that cause a harmful algal bloom. Human sources of excess nutrients (especially phosphorus) are one of the biggest components. These nutrients often enter lakes and rivers through sources, such as:

• Fertilizer runoff
• Failing septic systems
• Stormwater runoff from urban or industrial areas

Even when nutrient levels are stable, unpredictable weather conditions or changes in water flow can trigger blooms. For instance, a lake with normal nutrient levels in spring might still experience a bloom in summer due to a storm or urban runoff.

Our Water Quality program offers an annual Freshwater Algae Control grant for cities, counties, state agencies, Tribes, and special purpose districts to fund projects that prevent, remove, reduce, or manage excessive freshwater algae growth. For more information about the requirements and eligibility, view our Freshwater Algae Program Grant guidelines and previously funded Freshwater Algae Program grants.

How to stay safe around harmful algae

While laboratory testing is the only way to confirm if an algal bloom or mat is toxic, there are a few common characteristics to keep an eye out for. Avoid going into water that has the following characteristics:

• The appearance of slimy scum, foam, or growing clumps on the water
• Blue-green, reddish-brown, pea soup green colors
• A paint spill appearance on the water
• Swimming, fishing, and shellfish advisories

Possible signs that you or your pet may have been exposed to a harmful algal bloom include:

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

If you think you or your pet have been exposed to a harmful algal bloom, rinse off with clean water and seek appropriate medical attention. For additional information and guidance, please visit Department of Health's Harmful Algal Blooms Toolkit.

Local jurisdictions or the ‘lake manager’ make the determination on when to close a lake or recreation area due to toxic blooms, based on state Department of Health guidelines. While Ecology does not make these decisions, we help fund important parts of this work – the King County Environmental Lab that analyzes algae samples from across the state, the Washington State Toxic Algae website that hosts sample results, and the sharing of timely sample results via our Freshwater Algae email distribution list. To receive reports about current freshwater algal blooms in the state, join our email list.

“In addition to always paying attention to posted signage, I encourage folks to visit the Washington State Toxic Algae website” said Joey Teresi, Ecology’s Algae Control Financial Assistance Specialist. “It is a powerful resource to find information on your local lake and view toxin testing results.” 

What can we do to prevent harmful algal blooms?

While harmful algal blooms are hard to predict, there are steps you can take to reduce a water body’s chance of developing a bloom.

• Clean up and throw away pet waste.
• Choose phosphate-free detergents and soaps.
• Don’t over-water lawns and gardens.
• Maintain your septic system to prevent leaks.
• Do not feed waterfowl, like ducks and geese.
• Reduce or eliminate using fertilizer.
• Wash vehicles at a commercial car wash or away from storm drains.
• Maintain native plants around the lake or water body.

Though predicting harmful algal blooms is difficult, we all play a role in prevention and safety. With awareness and responsible practices, we can help protect Washington’s waters for everyone to enjoy.