Swimmer in the Forest

Deep in the forest was found the body of a man who was wearing only swimming trunks, snorkel and facemask. The nearest lake was 8 miles away and the sea was 100 miles away. How had he died?

Arvaus!

During a forest fire, a fire-fighting plane had scooped up some water from the lake to drop on the fire. The plane had accidentally picked up the unfortunate swimmer.