Weekly Update – Water Quality in Story County

July 23, 2021 –  Updated every Friday

 Fecal bacteria

E. coli bacteria is an indicator of fecal contamination. Not everyone who goes swimming or boating will swallow water, and not everyone who swallows water will get sick if there is human or animal waste in the water, but when E. coli is high, there is a greater risk.  Water quality may have changed since the last sample, so take greater precautions if it has rained recently and the water is murky.

… in Lakes

Going to the beach this weekend? The Iowa DNR monitors fecal indicator bacteria at Peterson Park and Hickory Grove Lake. Peterson Park is groundwater-fed so generally has low bacteria levels. Hickory Grove Lake is on the Impaired Waters List due to high E. coli levels and excessive algae growth in previous years but there has been extensive work to improve water quality.

Last sampled July 20: E. coli at Hickory Grove Lake was 310 colonies per 100mL, exceeding the recreational standard (less than 235 colonies/100 mL).

E. coli at Peterson Park was too low to detect, meeting the standard.

Going to a state park elsewhere in the state? Current beach advisories can be found here. The Iowa Environmental Council also sends out this data in a weekly newsletter.

kids at beach

 … in Rivers

 Rivers and streams in central Iowa frequently have E. coli levels above the state standard.  When enjoying paddling or fishing take some extra precautions to avoid accidentally getting river water in your mouth or on food.  We monitor 15 streams in Story County for nutrients and fecal bacteria, but keep in mind conditions change quickly and we can only monitor monthly.

 Most recent results from June 17: 3/3 sites we tested on the South Skunk River failed the primary contact recreation standard.

Water levels in rivers

To avoid dragging your canoe when paddling the South Skunk River, you’ll need at least 90-110 cfs at the USGS gage north of Ames.

The drought has been downgraded from severe to moderate in parts of Story County that got rain recently.  Ballard Creek was flowing again on Wednesday when I did my monitoring route, but the South Skunk and Ioway Creek have all but dried up.

The Skunk River Paddlers also have information about the South Skunk River water trail and links to current water conditions.

South Skunk at W Riverside Road / near Ames USGS Water-data graph for site 05470000, South Skunk near Ames, IA


Nitrate (a form of nitrogen) is a concern for the dead zone in the Gulf of Mexico. Prairie Rivers of Iowa and our partners have worked to promote practices in the Ioway Creek watershed that would reduce nitrogen and phosphorus loss. Before commercial fertilizers were introduced, nitrate levels in Iowa streams would have been less than 3 mg/L. While not relevant here, 10 mg/L is the drinking water standard.

 Current nitrate levels in Ioway Creek, from a sensor in the Iowa Water Quality Information System:

Nitrate levels have been low (below 5 mg/L) most of this year.  Unfortunately, we cannot attribute this to improved land stewardship–it’s the drought.  After heavy rains in mid-May, nitrate in Iowa Creek shot up above 15 mg/L, and gradually declined as tiles stopped flowing and river levels dropped.

Current nitrate levels in a drainage tile, near Kelley. Drainage systems provide a pathway for nitrogen to leach out of crop fields.