OUR GEM: Tackling Nonpoint Source Pollution in North Idaho, Protecting Coeur d’Alene Lake
Nonpoint source (NPS) pollution is a major environmental issue in North Idaho, particularly within the growing Coeur d’Alene Lake watershed. Unlike point source pollution, which stems from identifiable discharge points like pipes or ditches, NPS pollution is transported by diffuse sources such as rain or snowmelt. These waters pick up pollutants from urban areas, agricultural land, forests, and residential zones, eventually draining into lakes, rivers, and groundwater.
In North Idaho, multiple land-use activities contribute to NPS pollution:
- Urban runoff carries oil, heavy metals, and other contaminants from roads and developed surfaces into waterways.
- Agriculture contributes fertilizers, pesticides, and sediment from fields, while livestock operations can release excessive nutrients like nitrogen and phosphorus.
- Forestry and logging operations increase erosion, leading to sediment pollution that harms fish habitats and reduces water clarity.
- Legacy mining continues to affect the watershed, with heavy metals leaching from old mine tailings and contaminated soils.
- Residential development also plays a role, especially where failing septic systems, landscaping, and construction increase nutrient loads and erosion.
These pollutants have significant environmental and health impacts. Nutrients like nitrogen and phosphorus can promote harmful algal blooms, which deplete oxygen and disrupt aquatic life. Heavy metals and bacteria reduce water quality, while sediment disrupts habitats and drinking water sources.
To combat these issues, state and tribal agencies, conservation groups, and local communities have adopted a multi-faceted approach. Watershed Management Plans, Lake Management plans or Total Maximum Daily Load (TMDLs) implementation plans can be developed to help find target areas of nonpoint source pollution that could be reduced. These plans are often in conjunction with or related to TMDLs or “pollution budgets” that set allowable levels for contaminants in a waterbody while still maintaining water quality standards. Depending on the pollutant and water body, TMDLs can include suggested NPS reduction.
To meet these goals, Best Management Practices (BMPs) are implemented across land-use sectors:
- In agriculture, BMPs include planting riparian buffers, using cover crops, and applying fertilizers efficiently.
- In forestry, they involve erosion control, sustainable logging techniques, and replanting logged areas.
- In urban areas, methods like rain gardens, permeable pavement, and stormwater ponds reduce runoff.
- Homeowners are encouraged to maintain septic systems, use eco-friendly landscaping, and plant native vegetation along shorelines.
- Even the mining sector applies BMPs, such as mine waste stabilization and wetland treatment systems to manage contaminants.
A key funding source for NPS pollution projects is the EPA’s Clean Water Act Section 319 program, which supports education, technical assistance, and restoration work. In Idaho, the Department of Environmental Quality administers these funds to support impactful projects, such as stabilizing streambanks, fencing to keep livestock out of streams, and planting willows to reduce erosion. In the Coeur d’Alene basin, there have been various NPS pollution reduction projects. To learn more about NPS projects in Idaho, EPA provides a NPS project data explorer. The current federal 319 grant application period runs from April 15 to July 15, 2025.
As development in North Idaho continues, safeguarding water quality in Coeur d’Alene Lake and its surrounding tributaries will require sustained collaboration among state and tribal governments, conservation groups, and residents. By embracing BMPs and responsible land stewardship, the region can preserve its clean water and rich natural environment for future generations.
For more information on NPS pollution, 319 program and how to apply go to:
