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Flathead Lake is one of the largest bodies of freshwater in the western United States and has been characterized as a high quality, international resource. With an expansive watershed (18,379 km2) and lake surface area (496 km2) it is of outstanding aesthetic and recreational value. It also is extremely sensitive to both point and nonpoint source pollution. Recent growth and development patterns surrounding the lake have become an increasing concern. Impacts from permitted point sources, forestry, and agriculture are a challenge as well. In 1996, both nitrogen and phosphorus were identified as causes of impairment due to declines in lake clarity and nuisance algal blooms. Montana Department of Environmental Quality (MDEQ) released the Nutrient Management Plan and Total Maximum Daily Load for Flathead Lake in 2001 describing a two-phased allocation plan. Phase I established a short-term goal of reducing nutrient loading from the core urban and agricultural area north of the lake by 25%. Phase II was to refine the Phase I allocation through modeling. Given the magnitude and scope of the work, the importance of TMDL project planning has been paramount. Working cooperatively, MDEQ has developed an acceptable and feasible project management plan. This includes the implementation of an intensive data acquisition and monitoring program, construction of a basin-scale watershed loading model (LSPC), and development of several 2-dimensional lake models (CEQUAL-W2). Collectively, these tools will be used to support the TMDL allocations and implementation planning for the lake and surrounding area.