HARLAN - The Iowa Department of Natural Resources (DNR) is holding a public meeting on March 27 at 5:30 p.m. at the Harlan Public Library to discuss an upcoming alum treatment to improve water quality in Prairie Rose Lake.
DNR will present an overview of the proposed treatments and how this treatment will help reduce the frequency and intensity of harmful algae blooms (or HABs) in the lake.
Alum (aluminum sulfate) is a nontoxic substance used in everything from cooking to treatment of drinking water. It is commonly used to reduce phosphorus concentrations in lakes. Phosphorus, a key nutrient for algae growth, stems from runoff in the watershed.
While much of the phosphorus that ends up in a lake is buried in the lake sediments, it can also be recycled within the lake under the right environmental conditions and released from the lake sediments when bottom waters have no oxygen. These “internal releases” of phosphorus often fuel large algae blooms, especially in the late summer and early fall.
When applied to a lake, alum binds with the phosphorus in the water and settles as a thin flocculant on the lake bottom, where it will continue to inactivate phosphorus being released from the sediments. This process can significantly reduce the likelihood of HABs, which can be harmful to the ecosystem and limit recreation.
Prairie Rose Lake has experienced several blooms over the past few years. Recent research shows that watershed inputs and internal phosphorus recycling are driving these blooms, and a series of alum applications will likely help alleviate the frequency and duration of HABs.
The alum will be applied using specialized barges over a one week, between April 1 and May 15, depending on weather conditions. During this time, lake users may see boats, barges, heavy trucking equipment, and storage tanks around the park. DNR asks that you maintain a safe distance from the equipment to allow the crews to work efficiently.
There should be minimal disruption to regular activities on the water. The application dates were selected to minimize interference with spring fishing activities. No swimming or boating restrictions are anticipated.
DNR staff will be on site to monitor the application. This treatment is one part of a broader effort to continue to improve water quality and recreational opportunities at Prairie Rose Lake. An additional treatment is scheduled for Fall of 2025.
For More Information:
Michelle Balmer, Lake Restoration Program Coordinator, michelle.balmer@dnr.iowa.gov, Phone: 515.238.2458
John Lorenzen, Fisheries Biologist, john.lorenzen@dnr.iowa.gov, Phone: 712.769.2587