Otters disappeared from the Chicagoland area a century or so back as population and development surged. But now, they're coming back. The otter has made a comeback, Chris Anchor, chief biologist for the Cook County Forest Preserve District, said. "Almost all the watersheds in Cook County have otters. They're everywhere. They're kind of like the coyotes . . . there's definitely otters downtown." Anchor isn't sure where they're now coming from. They may have migrated from Wisconsin along the Fox and Des Plaines rivers, or traveled up north from the Kankakee River. They also might be traced to Louisiana. The Forest Preserve District plans to trap them and implant transmitters with the help of Brookfield Zoo, Anchor said. The devices will help track range, habits and lifespan. The animals will be checked for parasites, and blood and tissue samples will be taken for genetic studies.