by Jennifer Billock, Smithsonian.com

Wisconsin DNR

In the 1960s, Milwaukee had an alewives problem. The invasive fish managed to take over the rivers throughout the city and went completely out of control. They’d die off in mass numbers on the beach and cause a pretty awful smell, says Tim Vargo, manager of research and community science at Milwaukee’s Urban Ecology Center.

But the city had a plan to fix it. The Department of Natural Resources introduced salmon to the rivers to control the alewives, which are salmon’s preferred prey. And as a bonus, now locals would be able to enjoy a great sport fish.

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