Understanding Iowa Beach Advisories

The Iowa Department of Natural Resources (DNR) monitors all State Park beaches and many locally managed beaches in Iowa. Beach monitoring and sample collection is conducted weekly at 39 state-owned beaches in the summer, between Memorial Day and Labor Day. For current beach advisories you can refer to this website (https://programs.iowadnr.gov/aquia/Programs/Beaches) or call the DNR Beach Monitoring Hotline at (515) 725-3434, which updates its information every Friday in the summer. The DNR monitors these beaches for two sources of pollutants, E. coli and Cyanobacteria (blue-green algae toxins, also referred to as microcystins). E. coli is the most common impairment to Iowa’s lakes. If the beach has exceeded a water quality threshold for pollutants there will be a “Swimming is Not Recommended” sign at the site.  

On the DNR website referenced above the interactive map allows you to zoom in and out, and click on beach sites to access current water quality information.Yellow dots means that a water quality threshold has been exceeded and that “Swimming Not Recommended”. The green dot, “OK for swimming” means that all water quality standards for recreation have been met. The blue dot refers to local beaches that are locally managed and not administered by the DNR.  

The water quality threshold for E. coli can be exceeded if the geometric mean of 5 samples in a 30-day period exceeds 126 E. coli per 100 ml of water. In this case, the waterbody will be marked with a yellow dot and a “Swimming is Not Recommended” sign will be posted. The water quality threshold for E. coli can also be exceeded if a one-time sample exceeds 235 E. coli per 100 ml of water. However, a yellow dot will be used and a “Swimming is Not Recommended” sign will be posted only if the waterbody is considered vulnerable or transitional. That is why it is very important to click on the dot, regardless of color, to assess the beach status. Beaches that exceed the water quality threshold for microcystins, 8 micrograms per L, will also be marked with a yellow dot, and a “Swimming is Not Recommended” sign.  

Be sure to click on each dot on the map to receive more detailed information. Once you click on the dot a “Beach Status” popup will appear that gives you information about the last time the beach was sampled (or if it has not been sampled recently), the number of E. coli in the last sample, the geometric mean (or average) of E. coli found in the last 5 samples, and the amount of microcystin in the last sample. It is very important to look at the “additional info” section to see if results have exceeded water quality standards. For example, if the last sample for E. coli had elevated levels, but the water body is not considered nulnerable or transitional, the dot may be green instead of yellow. You will need to click on the “additional info” section to see if the following statement is included: “Result exceeds the single sample standard for E. coli.”  

The U.S. Army Corps of Engineers (USACE) Rock Island District conducts weekly monitoring at Coralville, Saylorville, and Red Rock lakes. USACE Rock Island monitors its beaches according to the same protocols as Iowa DNR. If there is a water quality advisory a sign will be posted at the beach. To see if there are any water quality advisories at these three lakes it is best to call them directly: 

Saylorville Lake: (515) 276-0433 (for automated water quality information) 

Lake Red Rock: (641) 828-7522 ext. 2 

Coralville Lake: (319) 338-3543 ext. 6300