MILWAUKEE (AP) -- Wisconsin Senator Russ Feingold says nothing should be off the table when it comes to saving the Great Lakes, even closing the St. Lawrence Seaway to ocean-going ships.

The Democrat says shippers need to know "we'll do what it takes to protect the Great Lakes."

Studies have shown ocean-going ships are bringing invasive species into the lakes in their ballast water. A study released this week says that is costing the region's economy at least $200 million per year.

The Seaway opened in 1959. While overseas shipping from the Great Lakes has dwindled, but the industry still says closing the waterway is unrealistic.

Feingold says he would prefer legislation requiring ships to treat their ballast water before entering the lakes to get rid of invasive species, but he is willing to consider a ban.