The Big Snowy Mountains are one of several island ranges found in central Montana, rising straight out of the prairie. But unlike the surrounding mountains in a mostly dry climate, this one has it's own lake. Crystal Lake is interesting for several reasons. It is very shallow and fish do not survive the winter when it freezes solid. The lake bed is made of porous limestone. The water level reaches it's maximum depth in early summer when the snow finishes melting. But then it starts to drain. As I walked along the shore I noticed the water bubbling away in certain spots as it seeped through the ground. By early fall the lake is significantly smaller and in some years it's not much more than a puddle. The color of the water also changes quite a bit depending on the direction and intensity of the sunlight. I liked this turquoise color the best as seen from an overlook called Promontory Point. Next time I visit I want to check out the perennial ice cave which is located at the top of the 8,000' ridge in the distance.