Feeding the lake is a stream running down from somewhere high in the mountains surrounding the valley. It winds back and forth up the steep slopes, and without proper equipment, most people would have a very difficult time following it for long. In some places, it narrows down to barely more than a trickle, in others, it widens to the point it could almost be considered a river (albeit a shallow one). It proceeds in a vaguely north-easterly direction, but follow the stream far enough, and you will encounter a particularly abrupt upswing in the trail's steepness, and a simple, stark sign warning not to proceed any further, or be fired upon.
