Use the navigation bar in the upper left corner of the map to zoom in and zoom out on Cass Lake. You can see satellite images of Cass Lake by clicking on "Satellite" or "Hybrid" in the upper right corner of the map.
Use your mouse to get GPS coordinates for any spot on Cass Lake. Simply click and drag the red arrow to the spot you are interested in and the geocodes (latitude + longitude) will appear in the boxes above - it's that easy!