Washington State Department of Health has developed guidelines for microcystins and anatoxin-a for those who manage recreational water bodies. The recommended recreational guidance value for microcystins is 6 µg/L and for anatoxin-a it is 1 µg/L. See the complete report, Recreational Guidance for Microcystins and Anatoxin-a (PDF 290KB, 25 pages).
Washington Lakes: Three-tiered Management Approach
The Department of Health developed a framework for managing toxic or potentially toxic cyanobacterial blooms using a three-tiered approach. For more on the framework, see Figure 1 and pages 9 – 12 of the report. The report describes when to take a bloom sample and when local health jurisdictions should post a CAUTION (Tier I), WARNING (Tier II), or DANGER (Tier III) sign.
|Tier I. A CAUTION sign is intended to provide the public with information that a public health hazard might exist. It is posted if a bloom is forming or a bloom or scum is visible.
|Tier II. A WARNING sign is posted if microcystins levels are 6 µg/L or higher and/or anatoxin-a levels are 1 µg/L or higher. The lake should be sampled weekly, at a minimum, with the WARNING sign posted as long as toxin concentrations remain above 6 µg/L (microcystins) or 1 µg/L (anatoxin-a).
|Tier III. Under certain circumstances, a local health jurisdiction may want to close a lake with unusually high microcystin or anatoxin-a concentrations. A water body can be posted as DANGER – Closed – at the discretion of the local health jurisdiction or appropriate agency. Examples include: very dense blooms covering an entire lake, confirmed pet illnesses or death, and reported human illness.
Search to see which water bodies have toxic algae blooms or report and have blooms tested through the Washington State Toxic Algae Website.