It's protected for nesting birds, hence the name Duck Island. But police are investigating unauthorized skateboarding after KING 5 notified them.

Seattle Police are investigating an unauthorized skateboarding spot on Duck Island in Green Lake. Seattle Parks filed a police report after KING 5 notified them of the structure.

"I thought it was made up. I don't know how folks got concrete and materials out there without being seen by other people. The parks department clearly doesn't want people out there because it's a safety hazard. We're more concerned with the natural resource value, but how they did it is beyond me. This is brand new to us," said Seattle Audubon Executive Director John Brosnan.

Seattle Audubon is a group committed to preserving bird habitat like Duck Island, so they were surprised to hear about a concrete skate bowl there. It's protected for nesting birds, hence the name Duck Island.

"I think the name says it all. It started out as a swan sanctuary and it's had nesting geese, nesting ducks and who knows exactly what else is livivng out there but that's the reason. We don't know. We're not supposed to be out there," Brosnan said.

This video shows what appears to be the project underway. KING 5 got a tip that amateur skate boarders built a bowl as a part of a Nike challenge to create unique skate parks. On the Nike website, the entry is tied to a Capitol Hill skate shop called 35 North. Workers there said they didn't build it but don't believe there aren't enough skateboard spots in the city.

"That's habitat in the city. That's what Seattle Audubon cares about. With so much urbanization and development going on it's important we preserve what nature is left in the city of Seattle," Brosnan said.

Duck Island was officially protected in the 1930s for swans. Though it has no formal protection anymore, Seattle Parks discourages recreational lake users from ever touching foot on it. Seattle Parks took these pictures of habitat damage today. Bird activists call it a loud intrusion on a rare oasis in an increasingly urbanized area.