OUR GEM: Tracking phosphorus in lake tributaries to protect Lake Cd’A
Photo courtesy of Our Gem.
Understanding how phosphorus enters and moves through Lake Coeur d'Alene is critical to protecting water quality and managing long-term environmental risks. According to Craig Cooper of the Idaho Department of Environmental Quality (DEQ), phosphorus plays a key role in influencing metal mobility in the lake. While nutrients like phosphorus support algae growth, the decomposition of that algae can reduce oxygen levels and pH in deeper waters, conditions that may trigger the release of metals from lakebed sediments. This connection between nutrients and metals makes phosphorus monitoring especially important in a system like Lake Coeur d'Alene, where legacy mining contamination remains a concern.
Tributaries that flow into the lake are a significant source of phosphorus and have become a major focus of recent monitoring efforts. DEQ and the Coeur d’Alene Tribe have previously estimated that these streams contribute an estimated 12 to 28 tons of phosphorus annually, accounting for roughly 6–16% of the total phosphorus load entering the lake. Their proximity delivers nutrients to the lake quickly, and in some cases, tributary inputs may include a higher fraction of bioavailable phosphorus, increasing their influence on lake productivity. At the same time, increasing development pressure in the region has heightened concerns about how land use changes may be affecting nutrient loading.
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