Monitoring the health of Lake Coeur d’Alene is a collaborative effort involving multiple organizations, each contributing important pieces to the bigger picture of the lake’s condition. Four key groups — the United States Geologic Survey, the Idaho Department of Environmental Quality, the Coeur d’Alene Tribe, and volunteers with the Bay Watchers program coordinated by the Idaho Water Resources Research Institute all play important roles in collecting data that helps track changes in water quality over time. 

Long-term monitoring by DEQ and the Coeur d’Alene Tribe 

The Idaho Department of Environmental Quality has been conducting year-round water quality monitoring since 2007, with temperature collection and other seasonal data going back to the 1990s. Their monitoring focuses on understanding trends in lake ecology, nutrient levels, and the presence of toxic metals like cadmium, lead and zinc. This long-term data provides essential insights into the health of the lake, including how it responds to cleanup and restoration actions along the Coeur d'Alene River, nutrient pollution, climate change and increasing recreational pressure. 

The Coeur d’Alene Tribe has been monitoring the southern portion of the lake since 2003 and since time immemorial. The Tribe has been focusing on water quality, nutrient dynamics and ecological health. These data play a crucial role in understanding how changing conditions, including warming temperatures and low oxygen events, also known as anoxic events, affect nutrient cycling and heavy metal releases from lakebed sediments. 

The role of the Bay Watchers program 

Since 2019, the Bay Watchers program has provided a valuable opportunity for local volunteers to help monitor water quality in nearshore areas and bays around the lake. This community science effort collects data on water temperature, clarity, dissolved oxygen and other parameters, helping to increase local awareness and provide useful information about seasonal conditions in specific locations. 

While the Bay Watchers data set is still relatively young, it offers an important complementary perspective, especially in shallow nearshore areas that may not be covered as extensively by the larger-scale monitoring programs. Shallow nearshore areas along the lake may respond quicker to some types of disturbance and can serve as early warning indicators for impending changes to the lake as a whole. However, the multi-decade data collected by DEQ and the Tribe is better suited for identifying long-term trends across the whole lake. 

What long-term data show 

Long-term monitoring by IDEQ and the Coeur d'Alene Tribe has shown that zinc and cadmium are declining north of the Coeur d’Alene River and that the lake’s biologic productivity is holding steady in the northern waters. The data also show a gradual warming trend in surface water temperatures over the past 30 years, consistent with rising air temperatures and broader climate patterns. Data review conducted for the 2022 National Academies of Sciences report, The Future of Water Quality in Lake Coeur d'Alene, found that surface temperatures at a key central lake monitoring station have increased by approximately 1.1 degrees Celsius over the past three decades. This warming trend is expected to continue in the future, which could have implications for lake mixing, oxygen levels and nutrient cycling. 

Recent reporting in the Coeur d'Alene Press highlighted that lake temperatures are warming, referring to comments made by Meg Wolf of IWRRI during a presentation to Bay Watchers volunteers. It’s important to clarify that the citation of warming trends is based on the long-term monitoring conducted by IDEQ and the Coeur d'Alene Tribe rather than the 2024 data update for a single monitoring season presented to the Bay Watchers volunteers. While the Bay Watchers program provides valuable seasonal data and engages citizen scientists, understanding long-term trends requires analysis of multi-decade datasets, like those maintained by IDEQ and the Tribe. 

Monitoring oxygen levels and nutrient dynamics 

Both IDEQ and the Tribe are also closely watching the conditions that contribute to anoxia — periods of low or no oxygen at the lake bottom. Anoxic conditions can release heavy metals from lakebed sediments, affecting both water quality and aquatic life.  

Collaboration for a healthier lake 

Together, the efforts of the USGS, IDEQ, the Coeur d’Alene Tribe and Bay Watchers contribute to a more complete understanding of Lake Coeur d’Alene’s water quality. Long-term, scientifically rigorous monitoring by USGS, IDEQ and the Tribe provides the foundation for understanding trends and changes across the whole lake, while Bay Watchers’ volunteer efforts provide valuable local insights and engage the community in protecting a cherished resource. Additionally, Bay Watchers data may provide early warnings to recent changes in the nearshore and embayment areas that are not regularly covered by the long-term monitoring program.  

Each of these monitoring efforts has an important role to play. Continued collaboration and data sharing among agencies, scientists, and the community will be key to ensuring the health of Lake Coeur d’Alene for future generations. 

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Meg Wolf is the Assistant Director of Idaho Water Resources Research Institute. Craig Cooper is a Limnologist with Idaho Department of Environmental Quality. Dale Chess is Senior Lake Limnologist with the Coeur d'Alene Tribe.

The Our Gem Coeur d’Alene Lake Collaborative is a team of committed and passionate professionals working to preserve lake health and protect water quality by promoting community awareness of local water resources through education, outreach and stewardship. Our Gem includes local experts from the University of Idaho — Idaho Water Resources Research Institute, Coeur d’Alene Tribe, Idaho Department of Environmental Quality, the Basin Environmental Improvement Project Commission, Kootenai Environmental Alliance, Coeur d’Alene Regional Chamber of Commerce and Kootenai County.