San Francisco veterinarian Dr. Frances Gulland is committed to saving sick marine mammals, but she’s also desperately trying to figure out what’s killing them.

The world's oceans are in trouble. Warming seas and man-made pollutants are combining to unleash toxic algae blooms that are decimating whales, sea lions and other marine mammals. In a high-action film, NOVA explores this crisis through the exploits of Dr. Frances Gulland, a San Francisco veterinarian who runs the equivalent of a West Coast ER for marine mammals. On a typical day, listless sea lions flop on their sides, too exhausted to lift their heads. Others are agitated. Another chews obsessively on a flipper. They are all victims of a marine neurotoxin made by an organism that feeds on algae. Dr. Gulland is committed to saving these sick animals one at a time, but she is also desperately trying to figure out what's killing them.