Two fish kills in Iowa among worst in four decades

Fish kills this year in Iowa streams that were caused by farm fertilizer and manure are among the largest documented by the state in more than 40 years.

The large fish kills happened in March near Red Oak in Southwest Iowa and in July near Paullina in Northwest Iowa. Both were related to agriculture.

The Red Oak kill happened when an estimated 267,000 gallons of fertilizer leaked from a tank at NEW Cooperative into the East Nishnabotna River.

Co-op employees had been working to unclog a distribution line from the tank and mistakenly left open a valve when they left March 8 for the weekend. The cooperative reported that warm temperatures that weekend allowed the fertilizer to flow while no worker was there.

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The spill killed nearly all the fish and other aquatic life for about 60 miles into Missouri. The fish kill ended where the Nishnabotna meets the Missouri River, which diluted the contaminated water.

The Iowa Department of Natural Resources estimated that about 750,000 fish died in Iowa. That is the fifth-largest on record since 1981, Iowa DNR data show.

The largest happened in 2001 near Algona in Northern Iowa. An ammonia pipeline breach killed about 1.2 million fish in Lotts Creek over the course of about 49 miles.

In 1989, about a million fish died in Coralville Lake when water runoff from melting snow that January likely carried farm chemicals, decaying plant material and manure into the Iowa River. The fish died because of low oxygen and high concentrations of ammonia.

The Iowa DNR has asked the Iowa Attorney General's Office to litigate the Red Oak spill because its administrative fine limit of $10,000 is too small. NEW Cooperative might also need to pay the estimated value of the fish, which was about $226,000.

The other large spill this year near Paullina was the result of a broken field drainage line.

On July 17, someone reported dead fish in Mud Creek. An investigation revealed that manure from Roorda Dairy had been sprayed onto a cornfield and went into a sinkhole caused by the damaged line. Dairy workers did not see the sinkhole because of standing corn.

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The manure flowed to the creek and killed an estimated 107,000 fish in more than 9 miles of the stream. That included more than 400 smallmouth bass.

"This one is significant, both in length and in the number of fish killed," said Mike Hawkins, a fisheries management biologist who investigated the incident.

The number of dead fish was the 20th-largest on record. The value of the fish was estimated at about $28,000, though the department has not levied a penalty against Roorda Dairy.

The Iowa DNR has investigated more than 1,000 fish kills in the past 43 years.

There have been at least 11 fish kill investigations so far this year, according to Iowa DNR data. That is less than last year's 14 but more than 2022's nine.

Another fish kill caused by people happened in January in Cedar Rapids, when a water line break in an unoccupied building leaked into McLoud Run. The treated water, which contains chlorine, killed more than 200 trout and white suckers.

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