Just call him Captain Planet. Native Seattleite Macklemore has pitched in to help clean up the city's extremely polluted river, The Duwamish, and he's doing so with a big ol' billboard.

"We are Seattle," the always hometown-proud rapper wrote on his website. "No bridge, boundaries or invisible man-made lines divide us. This is our home, our people and our community. This is our city’s only river, and I want to do my part to make sure that it’s safe for all that reside here. I stand in solidarity with community leaders and families who have organized for years to right this injustice."

The billboard -- which features Mack standing (maybe a little awkwardly) on the bank of the river -- was launched by the Duwamish River Cleanup Coalition (DRCC) and is intended to get the city pumped to save the river, its fishy inhabitants and those who live on its banks.

In 2001, the river was deemed a Superfund site by the EPA, a.k.a. "an uncontrolled or abandoned place where hazardous waste is located, possibly affecting local ecosystems or people."

According to Cross Cut, the EPA has proposed a $305 million plan that would clean 20% of the waste currently polluting the river. Mack -- along with the Duwamish River Cleanup Coalition -- is asking for more: namely for a cleanup that will protect the health of surrounding residents.

Yikes. I guess that explains why Macklemore's standing on the edge of the river rather than splashing around in it.