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Toxic Blue-Green Algae: A Threat to Iowa Beachgoers

Did you know that blue-green algae blooms are showing up more frequently in Iowa Waters? Find out how these blooms affect the health and safety of your family and your summer.Lake Okoboji

  • Blue-green algae can produce dangerous toxins.
  • Harmful algae blooms form in slow-moving water when fed by an over-abundance of nitrogen and phosphorous.
  • Appearance is a visible surface scum resembling spilled paint, pea soup or streaking of green lines on the surface.
  • Toxic algae can range in color from bright, iridescent blue to green, red or brown.
  • Toxic algae can produce a foul odor.

For more information, please review our fact sheet on toxic blue-green algae.

Know the Dangersdog

Blue-green algae secrete harmful toxins, including microcystin, that can cause a variety of health problems for people and pets. Knowing the risks can keep you and your family members safe during the summer.

  • Direct exposure can cause breathing problems, an upset stomach, rashes, other allergic reactions and even liver damage.
  • Children are at higher risk because they are more likely to ingest the water, and they usually play near the shoreline where algae blooms are often thickest.
  • Inhaling water droplets containing microcystin can result in a runny nose, eye irritation, cough, sore throat, chest pain, asthma-like symptoms or allergic reactions.
  • Dogs that swim in or drink the water can suffer serious harm or even death, sometimes in a matter of hours. Avoid letting them eat or roll in scums along the shoreline.

Results of DNR Monitoring of State Park Beaches for the Toxin Produced by Blue-Green Algae (Microcystin)

The Iowa Department of Natural Resources monitors 39 state park beaches weekly in the summer for microcystin, a toxin produced by some forms of blue-green algae. Warnings advising beach-goers to stay out of the water are posted when microcystin exceeds 20 micrograms (ug) per liter, the guideline established by the World Health Organization for recreational waters. The Iowa Environmental Council tracks these warnings and compiles them into a table showing warnings from year-to-year dating back to 2006 when monitoring for microcystin began, shedding light on trends and hot spots.


Each number represents a single time period where the beach exceeds the 20 ug/liter of microcystin (the toxin released by toxic blue-green algae) established by the World Health Organization for recreational waters. The symbol * represents a testing period where no data was collected at the beach (during 2008, a year of excess flooding, monitoring funds went towards flood-related monitoring.) 

Weekly Monitoring

This chart shows the results of DNR's weekly monitoring of Iowa state park beaches from Memorial Day through Labor Day.

Exposure to Toxic Blue-Green Algae

If you suspect you, your child or your pet have been exposed:

  • Shower or rinse off with clean water as soon as possible.
  • It is a good practice to always take a shower or rinse off children or dogs after contact with surface water, even if no warnings or advisories are posted. Many beaches are not monitored and microcystin can linger even if blooms are not visible. Other potentially harmful contaminants, such as bacteria and viruses may also be present.
  • In case of symptoms, seek prompt medical care - or veterinary care for a pet.

Data shown is from the Iowa Department of Natural Resources. The DNR conducts beach monitoring from Memorial Day until Labor Day at state park beaches. Many other public and private beaches not monitored by DNR are also susceptible to blue-green algae blooms. A map showing the most up-to-date beach monitoring information, which is posted on a weekly basis during the summer outdoor recreational season, can be found on the DNR’s website. You can also call the DNR Beach Monitoring Hotline at 515-725-3434 for weekly updates. In addition to microcystin, on the DNR’s website you can find beach advisory warnings from bacteria. For more information, please review our fact sheet about toxic blue-green algae.