Fred Walton, age 10, of Dallas, Texas, for his question:

Can a porpoise live in fresh water?

The common porpoise and his playmates travel the world oceans. The merry mariners often romp into bays and estuaries and far up wide rivers into brackish and fresh water. This small cousin of the giant whale has dozens of relatives other kinds of porpoises and members of the dolphin family. Most of them live in the salty sea and pay occasional visits to river estuaries where the water may be fresh or brackish. But some of them spend their whole lives in fresh water and never visit the salty sea.

The black finless porpoise enjoys life in coastal waters around Asia and Japan. But he is just as much at home in fresh water and often swims happily up a river for 1,000 miles. A porpoise cousin called the white flag dolphin inhabits the Tung Ting lake of China. This fresh water inland lake is 600 miles from the sea. Other river dolphins spend their lives in the Ganges of India and the Platte and Amazon rivers of South America. Most porpoises end dolphins can, it seems, survive in fresh water, at least for a while, and certain dolphins happily spend their whole lives in fresh water.