The Lake Helena Watershed is located in Lewis and Clark (68%) and Jefferson (32%) counties, within the Upper Missouri River Water Basin, encompassing 402,000 acres. Within the Lake Helena Watershed lie the Silver, Tenmile and Prickly Pear Creek subwatersheds.
The headwaters of these streams lie within the mountainous, forested lands of the Helena National Forest along the Continental Divide and the Elkhorn Mountains to the south.
All streams within the watershed eventually flow into Lake Helena and the Missouri River, passing through the Helena Valley on their way. Lake Helena formed after the construction of the Hauser Dam, which flooded the wetland area where Silver, Tenmile, and Prickly Pear Creeks converged.
The Lake Helena Watershed is a large and geologically complex area. Both natural and man-made environmental impacts vary across the watershed. These impacts vary depending on the geology, vegetative structure and climate (natural impacts), as well as the intensity and complexity of both historic and current land use practices (man-made impacts).