The lake Ojo del Inca has a diameter of about 100m and is about 30 degrees warm. There are eddy currents in the middle of the lake, which makes it dangerous to swim in there. At the edge of the lake you can swim without any problems. There is also a side pool where non-swimmers are safe. You can also pitch your tent directly at the lake.
Unfortunately, you are never alone at the lake, as an older man and woman live there. They are nice to you but pushy and ask for a "donation" of 20Bs. Of course, the use of the lake is free of charge! We still gave 10 Bs as the man was so nice to us. Unfortunately, the woman reacted very annoyed and insulted, which is why we fled.