Harbor porpoises are being seen more and more in the San Francisco Bay -- for the first time in about 60 years, according to KQED.
The porpoises -- averaging five feet long, smaller than most porpoises -- were last seen in number during World War II, when San Francisco was a major ship-making hub. With ship building comes pollution, of course, and that could have factored into the porpoises' departure.
One researcher, Bill Kenner, told KQED "I remember coming across the Bay Bridge when I was very young, and it would just smell."
Researchers and onlookers on the Golden Gate Bridge are seeing the porpoises in number, and snapping photos of the "puffing pigs" -- as they are referred to by old-time sailors who've heard their exhalations.
Researchers aren't sure as to why the porpoises have returned, but it could simply be that the water is cleaner and the usually shy swimmers have rediscovered the Bay.