State Standard
The bacteria standard for Iowa’s recreational waters consists of two components:
- A geometric mean standard based on 5 samples in a 30-day period (126 colony-forming units of E. coli bacteria per 100 mL of water).
-
A one-time maximum standard based on a single sample (235 colony forming units of E. coli bacteria per 100 mL of water).
State advisory threshold for Cyanobacteria Toxins (Blue-Green Algae Toxins)
The Iowa Department of Natural Resources, in partnership with the Iowa Department of Public Health (DPH), follows guidelines recommended by the WHO for monitoring cyanotoxins in recreational waters in order to safeguard public health.
- 20 µg/L total microcystins from any composite beach sample.
Posting of Signs/Advisories
All State monitored beaches are posted with Information Signs on indicator bacteria and blue-green algae toxins that provide general information regarding ways to reduce the potential health risk associated with swimming at public beaches. These signs will also inform the public of current monitoring efforts and ways to obtain the data.
Posting will only occur between Memorial Day and Labor Day (recreational monitoring season). Advisories are generally updated on Fridays of each week during the recreational monitoring season, but may be earlier or later in the week depending on the timing of holidays, sampling schedules and availability of laboratory results. All monitored beaches will be signed to “Watch / General Information” when an advisory is not in effect or when monitoring is not occurring.
Beaches that exceed Iowa’s geometric mean water quality standard for indicator bacteria (the geometric mean of 5 samples in a 30-day period exceeds 126 colony forming units of E. coli bacteria per 100 ml of water) will be posted with a warning sign that state, “Swimming is Not Recommended”.
Vulnerable and Transitional Beaches that exceed the one-time sample maximum water quality standard for indicator bacteria (235 CFU/100ml) will be posted with a warning sign that states,“Swimming is Not Recommended”.
Beaches that exceed Iowa’s advisory threshold level for cyanobacteria toxins (20 µg/L total microcystins) will be posted with a warning sign that state, “Swimming is Not Recommended”.
Advisories will remain in effect until the geomean for indicator bacteria drops below the water quality standard, the one-time sample maximum for indicator bacteria drops below the water quality standard, and the one-time sample maximum for Cyanobacteria toxins drops below the advisory threshold.
Beach Classes
Beaches are placed on “vulnerable” list if they have exceeded the geomean standard for
indicator bacteria two or more times in the previous five years. The list is reviewed annually to
update the beaches classified as “vulnerable”.
Beaches are placed on the “transitional” list if improvements have been observed with respect
to indicator bacteria levels. Beaches in the transitional classification will be eligible to be
reclassified to “non-vulnerable” if they do not exceed the geometric mean standard for one
year.
Beaches that have not exceeded the geometric mean indicator bacteria standard or only
exceeded the standard once during the most recent five years are classified as being “less
vulnerable” to experiencing prolonged or chronic problems with elevated levels of indicator
bacteria.