Beach Monitoring: Safe to Swim?
About Iowa beach monitoring
From approximately Memorial Day weekend through Labor Day weekend each summer, water management agencies conduct monitoring for microcystin and E. coli bacteria at Iowa lakes. This is a 15- or 16-week period each summer.
Since 2006, the Iowa Department of Natural Resources (DNR) conducts weekly monitoring for 39 state park beaches (see full list below).
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.
Some cities and counties arrange with DNR to test local park beaches for E. coli. The local managing department determines whether to issue an advisory based on the results provided by DNR.
When are swim advisories issued?
DNR and USACE Rock Island will issue swim advisories when:
- microcystin exceeds 8 micrograms/L
- E. coli exceeds state standards
The E. coli standard is exceeded when either:
- A geometric mean based on five samples in a 30-day period exceeds 126 colony-forming units per 100 mL of water
- A single sample exceeds 235 colony forming units per 100 mL of water
- DNR only issues an advisory for exceedance of the single sample threshold if the beach is classified as "vulnerable" or "transitional". More information on beach classification can be found on the DNR's website.
Iowa DNR and USACE Rock Island post a sign at the beach to indicate an advisory. DNR updates its beach monitoring website at www.iowadnr.gov/Things-to-Do/Beach-Monitoring.
Cities and counties can issue advisories for locally managed beaches by posting a sign.
Prior to 2020, microcystin advisories were issued at a less protective 20 microgram/L threshold.
The Iowa Environmental Council tracks the weekly beach monitoring reports and swim advisories from Iowa DNR and USACE Rock Island each summer. The results of our tracking can be seen below.
Every Friday during the summer recreation season, IEC sends Weekly Water Watch, an e-newsletter with beach advisory updates and other important water news.
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Trends in Swim Advisories
Microcystin-related Swim Advisories
Since the Iowa Department of Natural Resources beach monitoring program began in 2006, the number of annual swim advisories issued for microcystin has increased dramatically.
E. coli-related Swim Advisories
Overall, the number of annual E. coli-related swim advisories issued at Iowa State Park beaches has trended downwards in the last six years.
Notable Statistics from Summer 2022
- North Twin Lake West Beach experienced its first advisory for microcystin in seven years.
- With 14 advisories for E. coli and 2 for microcystin, Lake Darling was under a swim advisory for all but the week of June 17, the fourth week of the recreation season.
- Since 2014, Backbone has experienced the most E. coli advisories of all monitored beaches at 118.
- Four beaches recorded advisories for both E. coli and microcystin.
- 25 state park beaches recorded swim advisories this summer. 14 state park beaches did not record an advisory.
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