Eagle Lake Recreation Area, part of the Lassen National Forest, is 5,100 feet above sea level in northeast California and subject to harsh winter conditions. Having no natural surface outlet, Eagle Lake is a closed basin lake with its water levels fluctuating with variations of inflow. As temperatures drop below freezing, fascinating ice formations form on the surface. Photo by Bob Wick. Posted on Tumblr by the US Department of the Interior, 1/14/16.