EPA Recommends New Water Quality Standard for Microcystin

The Environmental Protection Agency recently published their recommendation for microcystin recreational water quality criteria. Microcystin, a toxic byproduct of blue-green algae, can cause significant illness to humans, pets, and livestock.

The recommendation is intended as guidance for states to consider when developing water quality standards; however, states can set water quality criteria that differ from the EPA’s recommendation.

The new recommended criterion is eight micrograms per liter. The EPA recommends a swimming advisory be issued when microcystin in a recreational water exceeds that level. 

A single exceedance of 8 micrograms/L would not necessarily indicate that a waterbody could not support recreation, but the EPA recommends that if the criteria is exceeded for a 10-day period, that would be considered an excursion from recreational criteria. If three “excursions” happened in a single recreational season in more than one year, the waterbody could be considered impaired.

Iowa’s Microcystin Standard

The state of Iowa does not have a water quality standard for microcystin. Therefore, a waterbody could not be considered impaired for microcystin because the standard has not been established. The IDNR does operate using a microcystin advisory threshold for of 20 micrograms/L, at which point a swimming advisory is issued. The waterbody remains open, but swimmers, boaters, and other recreation goers use it at their own risk. 

If we were to apply the EPA’s recommended criteria to the summer of 2018, there would have been an additional 11 swim advisories issued by the IDNR for a total of 17 swim advisories that summer. That's almost three times the six advisories issued at the 20 micrograms/L level in 2018! 

Microcystin has already been detected on state beaches this summer. The microcystin value for Green Valley Lake in Union County is already at 7.452 micrograms/L this week – just shy of the EPA's suggested threshold. View the report for beach advisories for this week. 

Updating Iowa's Standard

IEC urges the IDNR to develop a recreational standard for microcystin. We also ask that they critically evaluate the EPA's recommendation and the underlying science to determine if the swim advisory threshold should be updated to 8 micrograms/L.

More information about microcystin

Cyanobacteria (also called blue-green algae) are photosynthetic bacteria. On warm summer and early fall days when the water temperature is between 60 and 80°F, light is strong, and nutrients such as nitrogen and phosphorus are available, cyanobacteria can rapidly multiply and cause algae blooms.

Some types of cyanobacteria create microcystin, a chemical that is toxic to humans and animals. Human health symptoms include skin rashes, nausea, diarrhea, fatigue, and damage to the nervous system, liver, and kidneys. Symptoms can occur after direct contact with the water, ingestion, and inhalation of water droplets, which might occur during boating or other water recreation activities. Animals, particularly dogs, can experience acute exposure from licking cyanobacteria off of their fur.

Additionally, when the algae bloom decays, the decomposition process consumes oxygen and could cause a fish kill.

Learn more about algae and microcystin.

1. beach advisories
2. harmful algal blooms
3. microcystin
4. nitrate pollution
5. phosphorus pollution
6. public beaches
7. water quality