The Iowa Department of Natural Resources wants to change the way it measures bacteria in recreational waters, a move some environmental groups say could cause more people to get sick after swimming or boating.

“The issue is not just about reducing a regulatory burden or saving money,” said Susan Heathcote, water program director for the Iowa Environmental Council. “It is about setting a standard that will protect the quality of our recreational waters and, most importantly, protect the health of the people swimming at our public beaches and recreating in our rivers and streams.”

The DNR tests recreational waters for E. coli — a bacteria that can sicken swimmers — through two criteria.

One is the single sample maximum, which is 235 organisms per 100 milliliters of water for primary recreational waters, such as lakes used for swimming, and 2,880 organisms per 100 milliliters for secondary recreation waters.

The second criteria is geometric mean, which is the median level of E. coli in four samples on different days that can’t surpass 126 organisms per 100 milliliters.

If water samples show the geometric mean is too high, or more than 10 percent of samples exceed the single sample maximum, the DNR lists the water body segment on the impaired waters list required by the U.S. Environmental Protection Agency.

The DNR’s water quality assessment division has proposed eliminating the single sample maximum, which DNR Water Quality Bureau Chief Jon Tack said in a statement is “overly stringent” and “not an appropriate measure for water quality assessment and permitting purposes.”

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Roger Bruner, supervisor of the DNR’s water quality assessment section, said the single sample maximum can be misleading because a water body can be declared impaired after a one-day spike caused by a heavy rain, for example, that washed manure from nearby farm fields.

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“The geometric mean is a better measure,” Bruner said. “You don’t have one sample that is high, but you have consistently high levels over time. That tells Iowans there is more of a long-term problem.”

Single sample maximum still would be used in Iowa’s beach monitoring program, which tests all state beaches and many county and city beaches every week during the summer. Beaches with bacteria or blue green algae exceeding state standards are posted with an advisory to avoid swimming.

Critics of the rule change say it was intended to shrink the impaired waters list, saving face for the DNR and saving time in developing restoration plans.

“They’ve gotten so much criticism about the impaired waters list increasing every two years and they’re trying to find a way to reduce that,” said Wally Taylor, of Marion, who is legal counsel for the Sierra Club’s Iowa chapter.

Iowa’s 2016 draft list, released April 14, included 750 bodies of water with 1,096 impairments, up slightly from 736 lakes, rivers and streams with 1,062 impairments on the final list for 2014. One of every two water bodies tested for the 2016 list was impaired.

Twenty-two water body segments listed on the 2016 draft list would drop off under the proposed rules because those segments have no other impairment besides high single sample max tests, according to the DNR. This is 2.9 percent of all impaired waters on the draft list.

Heathcote said she’s concerned non-beach swimming locations, such as rivers or lakes used by paddlers, could see E. coli spikes without triggering restoration.

“They’re going to save some money, but at the expense of making the water riskier to the public,” she said.

To comment on the proposed rules changes, the public is invited to a hearing at 4 p.m. Sept. 5 at the Washington Public Library, 115 W. Washington St., in Washington, Iowa. Additional hearings that week are set for Urbandale and Harlan. Comments also may be made online at rules.iowa.gov/Notice/Details/3202C.

l Comments: (319) 339-3157; erin.jordan@thegazette.com