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DNR soliciting public comment on Big Hollow Lake improvement plan • Iowa Capital Dispatch [1]
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Date: 2025-05-06
The Iowa Department of Natural Resources has prepared a plan to improve water quality at Big Hollow Lake in Des Moines County and is now seeking public comments on the plan.
Big Hollow Lake was one of more than 700 segments on the DNR’s 2024 list of impaired waters in the state. The lake was impaired with high levels of algae, turbidity, or cloudiness, and pH, all of which have an impact on lake recreation and aquatic life.
Jim Hallmark led DNR’s presentation of the plan, which is available online until June 2, and said these issues are a result of excess nutrients, primarily phosphorus, entering the watershed and then the lake.
Per the Clean Water Act, states must develop Total Maximum Daily Loads, or TMDLs, for impaired waters, which is a calculation of how much of a certain pollutant is allowed in a body of water. From the TMDL, the state also determines a pollutant reduction goal and sets load reductions for identified polluters.
DNR records show Big Hollow Lake has been impaired since at least 2016.
The presentation included a pie chart of the share of existing total phosphorus, as it is allocated currently. Row crops account for 60% of the share. Hallmark said this is expected since the majority of the surrounding land is row crop farmland.
Nutrient runoff from row crops is considered non-point source pollution and is harder to regulate than point source polluters, who have permits with the DNR.
The existing phosphorus load for the lake is 7,414 pounds per year, and the TMDL goal is 2,188 pounds per year, or an approximately 70% reduction.
“Our objective is to reduce the sediment runoff in the watershed reaching our waterbody of interest,” Hallmark said.
He said reducing the phosphorus in the lake would decrease algal blooms and pH spikes.
The TMDL also outlines strategies to meet the reduction goals.
Some of the options for nutrient reduction in the watershed include land management practices like cover crops, manure and nutrient management, perennial strips and reduced tillage. These strategies would keep the nutrients on the land, closer to where they are applied.
Other options could include structural mitigation practices, like wetlands, buffer zones or sediment basins, two of which were installed near the lake in 2024. These strategies would help to trap some of the nutrients before they end up in the lake.
The final option could include in-lake remediation, including targeted dredging, where the water is lowered and sediment is removed from the bottom of the lake.
Locally, Des Moines County Conservation teamed with state and county partners to develop its own water quality project and encourage folks who live or own land in the watershed to implement some of the nutrient reduction strategies.
“You are the first line of defense for the lake’s water quality,” the county’s website reads.
Public comments on the DNR’s TMDL must be submitted by June 2. After the comments are collected, the department will forward the final plan to the U.S. Environmental Protection Agency for approval.
Public comments on the plan can be emailed to: [email protected]
Or mailed to: James Hallmark, care of Iowa DNR, 6200 Park Ave, Suite 200, Des Moines, Iowa 50321
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