This week, Woodland Park Zoo will release more than 80 western pond turtles into the wilds near Lakewood, Washington.

It’s been 22 years since the inauguration of the Western Pond Turtle Recovery Project, launched to save the endangered turtle; in 1990, their population in Washington had crashed to around 150.

Now, after two decades, there may be as many as 1,500 western pond turtles at six managed habitats in Klickitat, Skamania, Pierce, and Mason counties. Researchers believe the turtles’ brush with extinction was due to loss of healthy habitat, disease, and the appeal that baby turtles hold for ravenous, non-native bullfrogs.

Woodland Park Zoo is a participant — along with the Oregon Zoo — in what’s known as a “head-start” program for the turtles, in a partnership with Washington’s Department of Fish and Wildlife, and the U.S. Fish and Wildlife Service. Each fall, workers comb the turtles’ nesting ground for hatchlings and eggs, scoop them up, and deliver them to the zoos, where they can be fed and raised in safety. After ten months, they’re released again, now as big as 3-year-old wild turtles, and ready to rumble with any bullfrogs.

Studies on their survival rates support the head-start theory, but even so the population’s recovery will be measured in decades, because it takes the turtles about ten to 15 years to reach sexual maturity. (They can live 40 or 50 years.)