Oceangoing ships will need a state permit to enter Michigan ports starting in 2007 under a state law aimed at protecting the Great Lakes from exotic aquatic species.
Governor Jennifer Granholm has signed legislation requiring oceangoing ships to prove they will not discharge ballast water or are equipped to treat it.
A vessel takes in thousands of gallons of ballast water to stabilize the ship when traveling without cargo.
Ship ballast is widely believed to be a leading contributor to the problem of aquatic invaders from Europe or Asia.
A new invasive species is discovered in the Great Lakes at the rate of one every eight months.
The species can crowd out native species, cause environmental damage or bring new diseases.