How Much is Too Much of a Toxin? 

Algae blooms on Iowa lakes are not only unsightly and smelly, but can also lead to growth of cyanobacteria that produce a toxin called microcystin. People exposed to microcystin have reported acute effects ranging from abdominal pain to blistering around the mouth and pneumonia. Ingesting it makes people vomit. Dogs have died after swimming in it. 

The health threat posed by microcystin was part of the reason IEC created the Weekly Water Watch. We want to be sure everyone swimming, boating, and enjoying the water has the best information about what is safe. 

Iowa DNR started using a threshold of 20 micrograms per liter to issue beach advisories in 2006. Although the DNR only monitors a small fraction of recreational beaches in Iowa (just 39 beaches at state parks), the DNR still issued 217 advisories over the last 14 years. 

In May 2019, the EPA recommended an advisory threshold for the safe level of microcystin in recreational waters at 8 micrograms per liter (i.e., 8 parts per billion). Despite the new scientific guidance that the safe level was less than half its existing threshold, Iowa DNR decided it would keep using 20 for the rest of the year. IEC calculated that if DNR had used EPA’s threshold last year, there would have been 14 additional beach advisories. 

We called for DNR to start using EPA’s recommendation last year because the science showed people became sick from microcystin concentrations at DNR’s threshold. Several very popular lakes had significant algae blooms resulting in beach closures last year, including Lake Macbride, Spirit Lake, and Lake Rathbun. Avoiding the problems from microcystin seems particularly important during the current pandemic, when a person’s underlying health conditions may increase the effects of COVID-19. 

On May 20 this year, DNR revealed via an update to its website that it will start using EPA’s recommended value, just as IEC had advocated. This is a big win for the public, letting us better understand the risks on Iowa beaches. 

However, IEC learned that DNR is treating some microcystin test results above 8 as a “provisional” advisory. Last week, DNR stated that a sample greater than 8 was “outside the linear range of the test” and DNR would re-test to determine a final value. For all provisional advisories issued, DNR will post a beach advisory for the week and re-test the sample. We are glad that DNR is taking a protective approach to public health, but we are also investigating DNR's use of provisional advisories and testing methods in regards to the linear range of the tests.

As we move into summer, please remember to pay attention to beach advisories – for your own safety. Remember that only the beaches monitored by DNR will have signs posted. You can find more at the Iowa DNR website. 

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