EPA Releases Water Quality Criteria to Address Harmful Algal Blooms in Recreational Waters

June 20, 2019

The U.S. Environmental Protection Agency (EPA) released new national guidance on May 22, 2019, to help state agencies protect the public from recreational exposure to certain types of harmful algal blooms (HABs). The new release provides human-health-based numeric ambient water quality criteria for two toxins, microcystin and cylindrospermopsin, which can be produced by cyanobacteria, commonly called blue-green algae. The threshold values are 8 µg/L for microcystin and 15 µg/L for cylindrospermopsin. EPA recommends 10-day assessment periods over the course of the recreation season. If the criteria are exceeded once during an assessment period, then EPA recommends increasing monitoring frequency; exceedances during more than three 10-day periods during the recreation season indicate that the water quality may be degraded. Any single-day exceedance of these values should trigger a swimming advisory.

These national recommendations supersede a draft previously published in 2016. The criteria are recommendations for states to consider as the basis for swimming advisories for notification purposes; they are not legally binding regulations. In cases where local recreational water body managers have limited resources, EPA recommends developing a risk management plan to identify and prioritize water bodies that are either at risk of HABs or that, if overtaken by toxic HABs, would have a significant impact on the public.

How Exponent Can Help

Assessing whether a particular water body is vulnerable to HABs often requires site-specific investigation. Exponent scientists and engineers can help water body managers prioritize vulnerable waters and develop an effective HAB monitoring plan. We can help evaluate information characterizing the historical occurrence, frequency, and geographic extent of HABs and identify appropriate site-specific early-warning indicators, such as biological indicators, water chemistry parameters (e.g., nutrient levels), and hydrological and meteorological conditions.

Additionally, Exponent's expertise in the environmental and human health fields can be applied to:

  • Evaluating and interpreting cyanotoxin monitoring results to assess risk when concentrations of cyanotoxins are approaching the recommended threshold levels.
  • Interpreting concentrations of cyanobacterial species or cyanotoxin-associated genes using molecular methods.
  • Evaluating the influence of changes in chemical, hydrological, or meteorological conditions on potential HAB occurrence and HAB movement.
  • Assessing the cause(s) of HABs in association with land-use or discharge scenarios.