Hauser Lake is a 3,270 acre manmade reservoir created by Hauser Dam near a small branch of the Missouri River. It is located about 5 miles north of Helena, Montana. The lake itself reaches depths of over 100 feet.
The lake is located in Hauser Lake State Park between two popular beaches, affectionately titled "White Sandy" and "Black Sandy" for the disparate colors of their sandy shores. It also connects to the even larger Lake Helena. It is an excellent area for camping, boating, watersports, and perhaps most importantly fishing. Salmon, walleye, rainbow trout, and perch are kept well-stocked in the waters.
In the winter, Hauser Lake like most northern lakes freezes over, but this doesn't stop it from being a popular vacation spot. Ice skating and ice fishing continue unabated.
(My Internet research has led me to the interesting fact that there is also a Hauser Lake in both Idaho and Texas. I've lived in Texas most of my life, and I've never been to the local one. But the Montana one is gorgeous, and highly recommended.)