Spring Water Quality Snapshot, 2025

Testing of multiple sites within a short time period can provide a “snapshot” of water quality across a watershed, county, or state. Volunteers in central Iowa tested 162 sites on May 20 and May 21.

• Polk County Conservation organized testing of 117 sites on May 20. Water samples were also collected from 32 sites and analyzed by a certified lab.

• Prairie Rivers of Iowa organized testing of 28 sites in the Ioway Creek watershed on May 20, in Story, Boone, and Hamilton counties. Ames High School earth sciences classes participated on both May 20 and 21; retesting sites near the high school helped us identify a problem with expired nitrate strips and check if water quality in Ioway Creek had changed from one day to the next (not much).

• Story County Conservation encouraged volunteers to schedule their biweekly testing to coincide with the snapshot. 6 sites were tested on May 20 and 11 sites were tested on May 21. Water samples were also collected from 15 sites on May 21 and analyzed by a certified lab.

Highlights

• Water quality was tested after heavy rains and shows the influence of both urban and agricultural runoff.
• Nitrate levels in Story County measured by the lab were the highest we have observed since we began regular monitoring in 2020, reaching 30 mg/L at one site. Several rural streams in Polk County also exceeded the drinking water standard (10 mg/L). Volunteer testing also showed high nitrate levels but the results are less precise.
• Urban streams like Yeader Creek in Polk County had much lower nitrate levels than rural streams but higher chloride levels.
• Most streams exceeded secondary contact standards for E. coli, both in rural and urban streams. This suggests there are multiple, widespread sources of fecal contamination, flushed into the river by rain events. E. coli can come from any warm-blooded animal including humans, pigs, cows, poultry, geese and other wild birds, dogs, and raccoon.
• Most streams had muddy water (low transparency), suggesting widespread sources of erosion (which could include the stream channel itself). Storm sewer outflows sometimes had clear water, however we saw evidence that urban stormwater runoff is contributing to bank erosion downstream.
• A beaver was spotted in Beaver Creek!

Results from field tests

Volunteers and city and county staff in Polk County and in Story County use different databases and training materials, but the equipment and methods used to test water chemistry and physical properties are almost identical. Results are shown as an interactive map. The color coding matches the scheme used on the Izaak Walton League’s Clean Water Hub. However, our transparency tubes only have markings to 60 cm and our chloride titration strips have a lower limit of 28-30 mg/L, so the threshold for “excellent” was adjusted to match those detection limits.

• Green = Excellent

• Yellow = Good

• Orange = Fair

• Red = Poor.

• Gray = Not tested.

Zoom in and click on a site to get a pop-up window with more detailed results. If pop-ups don’t respond, try toggling between water quality metrics first. Note that start times may be recorded as AM/PM or military time.

Results from laboratory analysis

Water samples were collected from thirty-two sites in Polk County on May 20 and analyzed by the Des Moines Water Works for E. coli, nitrate, phosphorus-O as P and chloride.

Fifteen sites in Story County were sampled on May 21 and tested by the City of Ames laboratory services for E. coli, nitrate, total phosphorus, and total suspended solids.

Color coding for nitrate, phosphorus and chloride is the same as the map above. Color coding for E. coli is red for samples exceeding the secondary contact recreation criteria (2,880 colonies/100mL) and yellow for samples if they exceeding the primary contact recreation criteria (235 colonies/100 mL). Note that Story County tested total phosphorus, so results will be higher than Polk County, which measured only dissolved forms of phosphorus. Phosphorus results below the detection limit in Polk County were omitted and shown as gray on the map due to a data formatting issue.

Weather and water levels

A band of storms passed through central Iowa the night before the snapshot event, with skies clearing by mid-morning. The weather station at the Des Moines airport recorded 4.9 inches on May 19 and 20. The station at the Ames airport recorded 3 inches of rain on May 19 and 20. Some areas also received light rain late evening on May 20.

Most of the testing in Polk County was done between 9AM and 12PM on May 20 when rivers were either cresting or had dropped since earlier in the morning. Some volunteers noted that creeks were out of their banks, moving fast, and very muddy.

Water levels at Beaver Creek show a sharp rise and fall, which is consistent with runoff from paved surfaces.

In contrast, rivers in Story County continued to rise until the May 21 and were slower to come back down. This reflects the influence of runoff and drainage water from Hamilton county, which took some time to reach the gages.