The Lake Erie watersnake population had declined to about 1,500 adults by the mid-1990s because of human persecution and habitat loss from shoreline development. Federal and state agencies designated 300 acres of inland habitat and 11 miles of shoreline as breeding and hibernation grounds, while scientists led a public relations blitz to convince people the snake was nothing to fear.

The effort quickly paid off. By 2002, the snake had reached the government's minimum goal of 5,555 snakes. A census in 2009 estimated the population at nearly 12,000.

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Exotic species generally are regarded as harmful to ecosystems they invade. The round goby has caused a number of native Great Lakes fish to decline. But it arrived just in time for the watersnake.

"This is an ironic example of where an invasive species actually helps fuel the recovery of an endangered native species," said Kristin Stanford, a Northern Illinois University researcher who also works for Ohio State University's Stone Laboratory on Lake Erie's Gibraltar Island. "Within the past decade, watersnakes are now growing faster, bigger, with more offspring and a higher survival rate."