Testing of multiple sites on the same day can provide a “snapshot” of water quality across a watershed, county, or state. The spring 2024 snapshot showed how muddy Iowa rivers and creeks can get after heavy rains!

Participation

Five groups across Iowa participated in a water quality snapshot event, held on Tuesday, May 21.

Weather

On May 21, multiple rounds of thunderstorms brought hail, tornadoes, and flash flooding to state. More details about severe weather can be found here. Some volunteers were able to safely test their assigned sites during breaks in the weather, others had to postpone sampling. The areas tested for the snapshot received between 1.5 and 4 inches of rain on May 21 and the two days prior.

Results from field tests

Results for May 21, as well as the day before and the day after, are shown in an interactive map. Use the radio buttons to select which water quality metric is used for color coding. The color coding is almost the same as used on the Izaak Walton Leagues’s Clean Water Hub. However, we use 60 cm transparency tubes and chloride bottles with a lower limit of 28-30 mg/L, so the threshold for “excellent” was adjusted so as not to be out of reach. pH was omitted, as there was little difference between sites (all 7 or 8).

Zoom in and click on a site to get a pop-up window with more detailed results. (Comments for Polk County sites could not be included). If pop-ups don’t respond, try toggling between water quality metrics first.

Results from laboratory analysis

Polk County Conservation staff also collected some water samples that were analyzed by the Des Moines Water Works for E. coli, nitrate, phosphorus-phosphate and chloride. Color coding for nitrate, phosphate and chloride is the same as the map above. Phosphate results below the detection limit were omitted and shown as gray on the map due to a data formatting issue. 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).

Water Levels

Water levels in smaller creeks were rising on the morning of May 21, peaking later in the day or overnight.

The North Raccoon River near Jefferson continued rising through May 23.

Changes in water quality over time

A few sites in Ames were tested twice that week and can show how water quality changed in response to the storms.

Worrell Creek at S 16th St in Ames was tested on the morning of May 20 and again on the morning of May 21 (when water levels were rising). Transparency decreased from 55 to 2 cm, phosphate increased from 0.2 to 1.0 mg/L and nitrate increased from 5 to 10 mg/L. However, dissolved oxygen and pH were unchanged and chloride decreased from 43 to 30 mg/. Ioway Creek at 6th St showed similar results.

A tributary of Worrell Creek at the Tedesco Environmental Learning Corridor in Ames was tested at noon on May 21 (when water levels were rising) and again on the morning of May 22 (when water levels were falling). Phosphate dropped from 2 to 0 mg/L, nitrate decreased from 5 to 2 mg/L, and transparency increased from 7 to 15 cm. Chloride remained below the detection limit and dissolved oxygen stayed the same.

Real-time nitrate sensors showed that not all streams had the same water quality response same way to storms. Nitrate dropped from 14 to almost 0 mg/L on Tuesday in the Raccoon River at Van Meter, showing a dilution effect. Nitrate in the North Raccoon River near Jefferson remained high (staying between 17 and 19 mg/L) as water levels rose.