Crater Lake is the caldera of a volcano that blew the top off Mt. Mazama about 7500 years ago. over time, it filled with water from melting snow. there are no rivers in or out. the lake maintains approximate equilibrium because the amount of water gained from snowmelt each year is about equal to what it loses through evaporation. it's the deepest lake in the US, at 1940 feet, and the water is so clear that a tester, called a Secchi Disk, can be seen from the surface to a depth of 140 feet. it's about 5 miles in diameter, and takes a multiple-frame panoramic to get it all in. and yes, the water really is this blue... Canon 30D, 17-35 lens at 17mm, 1/30 @ f/14...
here's the panoramic view - 5 frames taken with the 17mm lens, stitched with Arcsoft PMK3 software...
here's the panoramic view - 5 frames taken with the 17mm lens, stitched with Arcsoft PMK3 software...