Swimming -- going into the lake at all -- is allowed only in one small place. Fishing is strictly restricted. It is one of the deepest fresh-water bodies in the world and the few who have had the chance to go report that its depths are breathtaking; and yet recreational diving is strictly restricted too. There is one boat which is allowed on the lake twice a day for excursion tours and it is a very special boat that makes almost no emissions and very little noise. Camping and hiking in the park are also limited.
Crater Lake is a place of amazing natural beauty and is, thankfully, being kept that way.
The idea of tourists with all of their detritus frolicing in Crater Lake, the thought of people on water skis and kids running around on jet skis on Crater Lake would make any Oregonian vomit.
Crater Lake is truly one of America's greatest treasures. It is one of the most beautiful places on earth.
Furthermore, it is a volcanic crater filled most of the way up with water. So, there is no real "beach" to speak of. In most places, the steep slope of the crater just goes right down into the water. This also means that there aren't a lot of "shallow" places where it would be safe for children to play in the water. Why it doesn't fill all the way up is a mystery. It has no surface outlet and rainfall and snow melt runoff exceeds surface evaporation. It may very well have a "drain" at the bottom. Where such a "drain" would drain to is a matter of some spaculation. Also, since the lake receives a great deal of runoff from melting snow each spring and because it is do deep and massive, the water is quite cold.