They put copper in anti-fouling paint for boats, and that does inhibit marine plant growth. In 'olden times' they used to sheath the bottoms of sailing ships in sheets of copper for that purpose and to protect wooden hulls from barnacles and ship worms. Copper is also a component in algaecide used in swimming pools to keep algae growth down.
Here's an article on it:
http://copperantifouling.com/c...
Scroll down to point #5 on Environmental impacts if you don't have the patience to read the whole thing.
