Lake CDA Committee Begins Work To Reduce Phosphorus Pollution

Aug 25, 2021

Idaho Governor Brad Little's handpicked committee to consider remedies to Lake Coeur d'Alene's phosphorus pollution problem will begin meeting Thursday.
Credit Courtesy of Idaho Department of Environmental Quality



Idaho state officials say they want to move quickly on projects that reduce phosphorus pollution in Lake Coeur d’Alene. Phosphorus promotes the growth of plants that can be toxic to humans and animals.

An advisory committee appointed by the governor to vet and choose proposals began its work Thursday in Coeur d’Alene.

Several lakes in north Idaho have major outbreaks of algae caused by high levels of phosphorus, which leaches from things like fertilizer and animal waste.

Lake Coeur d’Alene is not yet one of those lakes, says Craig Cooper, who monitors aquatic ecosystems for the Idaho Department of Environmental Quality.

“We keep it that way by having low levels of nutrients, nitrogen and phosphorus, in the runoff from the rivers and the land surfaces. With low levels of nutrients, we have a relatively low level of plankton and algae in the lake’s surface water," he said.

But with all of the development around Lake Coeur d’Alene and the rivers that feed the lake, Cooper says phosphorus levels are rising. That’s the focus of the lake’s new advisory committee, which is tasked with authorizing some preventive maintenance by choosing projects that will lower those levels.

Cooper says the projects may include concrete actions, such treating wastewater that’s piped into a waterway or taking steps somewhere to reduce soil erosion. Or, he says, it could be something indirect, such as changes to zoning or planning rules.

“When you’re building a new development, how do you manage the runoff from the water that comes into your development? When you’re building roads, how do you manage your swales for your stormwater in the runoff for your roads?” he said.

Managing Lake Coeur d’Alene’s phosphorus level is just one piece of the bigger puzzle of monitoring the water quality and all of the toxic metals that sit on the lake bed. Cooper says more phosphorus could lead to changes in the water’s chemical structure. That could bring those heavy metals back up from the bottom and potentially lead to changes in the way people use the lake.

The advisory committee is scheduled to begin reviewing phosphorus-reduction projects at its next meeting later this fall.