Aug. 3, 2010
Summertime algae blooms!
Summer’s idyllic dream of swimming in warm, clear water can sometimes turn into an unpleasant reality of nasty smelling algae along the shoreline.
Green algae at Madrona Beach, Lake Washington
Excessive algae growth can be stimulated by sunshine, warm water temperatures and lots of available nutrients, leading to blooms that can take the form of water cloudiness, floating scums, stringy mats, puffy cushions and underwater towers of greenish goo.
In King County, certain lakes produce algae nuisances every year, while others may have a problem only sporadically. This year, algae blooms have been reported from lakes Sammamish, Washington, Horseshoe, Hicks, Wilderness, Walker and Echo.
Different species of algae can be responsible for producing nuisance blooms, and the health and safety risks that accompany their success varies with the type that wins the summer growth competition.
Here’s a quick tutorial on what you might be seeing in your lake. However, there is no substitute for calling county staff or the State Algae Program to find out if what you are seeing may be a bigger problem than you thought.
Green algae at Magnuson wetland
Green algae blooms
If the algae mass is stringy and can be picked up and handled, it is probably filamentous green algae. Accumulations of filamentous green algae have been observed at swimming beaches on Lakes Washington and Sammamish. This green algae grows as filaments attached to rocks and the bottom substrate.
Sometimes they will also form floating cushions and mats, often with a puffy appearance. In a typical year the accumulations are noted along the shorelines beginning in mid to late July, but this year there have been reports coming earlier than normal.
Wind and wave action break off the long green algae mats so that they float free and accumulate along the shore. Though generally harmless, the decomposing piles degrade nearby water quality and can give off a pungent odor similar to that of decomposing lawn clippings. Green algae, or Chlorophytes, do not produce toxins like some cyanobacteria (also known as blue green algae).
Green algae sculpture at Madrona Beach, Lake Washington
Lakeside homeowners who find piles of stinky algae blooms along the water’s edge can rake accumulations into piles and add them to the yard waste bin. For more information on preventing algal blooms, please visit the links at the bottom of this page.
Blue-green algae blooms
Cyanobacteria, formerly called "blue-green algae," are simple life forms closely related to bacteria that resemble true algae. When conditions are right, blue-green algae will bloom and can turn lake water turbid with green, blue-green, or reddish-brown colored algae. Some blooms will form a thin oily looking film or scum on the surface of the lake. The film can look like a paint spill, as shown in this picture of Shadow Lake.
Blue-green algae bloom at Shadow Lake near Maple Valley
Blue-green algae blooms with toxin levels high enough to prompt warning signs or temporary closures occurred in 2009 in Lakes Echo, Hicks, and Wilderness. A similar closure occurred at Tuck Lake in 2008. These lakes, as well as eight others in King County, are being monitored in through 2011 as part of a risk characterization grant from the Centers for Disease Control (CDC) to discover how often regional lakes harbor blue-greens that produce toxins. While several lakes have tested positive for toxins this year, the levels have been too low for warning signs to be installed.
In the fall of 1997, a toxic bloom of the cyanobacteria, Microcystis aeruginosa in Lake Sammamish led to advisories at Lake Sammamish State Park, Idylwood Park and Marymoor Park. In 1999, Green Lake was closed to swimming because of a toxic algae bloom. Cyanotoxin monitoring has been a part of the King County Swimming Beach Monitoring Program since 2005, and 2010 data can be found on the King County swimming beach website.
Cyanobacteria can produce toxins that are potentially lethal to people and animals. Some cyanobacteria produce liver toxins and others produce neurotoxins, which can manifest from minutes to days after exposure.
In people, symptoms may include numbness of the lips, tingling in fingers and toes and dizziness. Liver toxin poisoning may take hours or days for symptoms to appear. Symptoms of liver toxin exposure include pain, diarrhea and vomiting in humans and death in animals.
In animals symptoms from neurotoxin exposure include weakness, staggering, difficulty in breathing, and convulsions.
Report algae blooms
The Washington Department of Ecology (Ecology) offers a freshwater algal identification and toxicity-testing service for Washington state residents and County Health Districts in Washington State. For more information about this program visit the State Freshwater Algae Control Program web site (external link).
Report illnesses related to swimming beach usage
The State Department of Health is collecting information on human and animal illnesses related to exposure to potential harmful algal blooms. This information is shared with the CDC. If you have concerns about pet or human illness after visiting your beaches, please refer them to:
What causes algae to bloom?
In lakes Washington and Sammamish, algae will grow more abundantly where there are high concentrations of phosphorus – a nutrient found in fertilizers, septic and other waste treatment systems and stormwater run off. Check out some of the King County Lakeside Living web pages listed at the top of this page for tips on how to help prevent algal blooms.
For questions about lakes in King County, please contact Sally Abella, senior engineer, or Debra Bouchard, water quality planner, Lake Stewardship Program.