Chuck MaLravy, age 14, of Lansing, Mich:

How does oxygen get into the water?

Water, of course, is a compound of oxygen and hydrogen. Its tiny particles contain atoms of oxygen and hydrogen, but the compound is very different from its parent gases. The oxygen breathed by fishes and other sea‑dwellers does not come from the oxygen locked in particles of water. It is free particles of gaseous oxygen mixed with the water and it gets into the water along with several other gases from the air.

Water gathers gases when it splashes around or tumbles through the air. This is why the fishes are more frisky in bubbling streams, around rapids and waterfalls. Ocean fish are most plentiful where oxygen is mixed into the water by rough waves and tossing tides. In certain still and stagnant seas there are no fish at all because there is no oxygen mixed with the water.