Toxic Bloom in Lake Sammamish

On September 18, 1997, an algae bloom of Cyanobacteria, a primitive life form known as "blue green algae", was found in the lake. Blooms - rapid, exponential growth - can produce a toxin that is a health risk to humans and potentially lethal to animals. In Lake Sammamish the toxic bloom lasted from September 18th to October 9th. The toxicity had spread over the lake within a week. Warning signs were posted at Lake Sammamish State Park, Idylwood Park and Marymoor Park. The media informed citizens about the bloom.

Health effects only occur if the toxin is ingested; it cannot be absorbed through skin contact. Poisoning symptoms may take 30 minutes to 24 hours to appear. Symptoms may include jaundice, shock, abdominal pain and distention, weakness, nausea, vomiting, thirst, rapid or weak pulse. No human deaths have been attributed to poisoning from this bacteria. Children and pets are at greater risk as smaller doses can prove harmful.

A bloom of this type is always a risk in any lake that receives high nutrient loads. In Lake Sammamish the right conditions: sunshine, warm water (72 - 80 degrees), no wind and high phosphorus produced the bloom. The best protection against the blooms is to reduce phosphorus inputs to the lake.