The kunimasu salmon, also called the black kokanee, is a subspecies of sockeye salmon that's found only in Japan. Unlike true sockeye, which migrate between freshwater and the oceans, the many types of kokanee salmon live and reproduce entirely in lakes.

The kunimasu was believed to have been wiped out in the 1940s after a hydroelectric dam raised acidity levels in the fish's only home, Lake Tazawako (map) in northern Japan's Akita Prefecture. Salmon are sensitive to water's acidity, and drastic changes in pH can affect young salmon's survival.

(Related: "Dams Not Main Cause of Salmon Collapse, Study Says.")

A seemingly unsuccessful