YOu are right it is amazing to keep such beauty of nature well preserved, the people probably love their place so much that try to keep it clean and clear. I have seen few lakes but not so clean that this on your photogrpahs, but since I am an adult I did not swim outside of swimming pool, on one hand I do not like chilly water, on the other I am not good swimmer, may be that is the main reason :)
I think it's more of awareness and concern to the environment
we only have one planet to live for now
no earth #2 has been found so far
not exactly like what we have
if we don't take care of it
with the knowledge that it could get ruined if we just treat it carelessly
then we should prepare living in Mars
but that plan sounds costly isn't it
you should take us around Scotland ..
they sure have such beautiful places out there, too imho