Conservationists and Great Lakes state residents are hailing a recent ruling from the Ninth Circuit Court of Appeals as a significant step toward fighting the spread of aquatic invasive species.

The state of Minnesota acted as a petitioner-intervener in Northwest Environmental Advocates v. EPA. The ruling (.pdf) upheld lower-court rulings that the Environmental Protection Agency overstepped its authority in 1973 by exempting marine discharges of ballast water from the permitting system established by the Clean Water Act.

Beginning Sept. 30, 2008, oceangoing vessels will no longer be able to discharge ballast water into the Great Lakes without an EPA permit. The Duluth News-Tribune reports the Minnesota Pollution Control Authority will proceed with its own ballast water regulations for Lake Superior based on the ruling. The MPCA will have its own permitting process in place for ballast discharges in Lake Superior and eventually require ships to clean their ballasts before entering the lake.

It is estimated that ballast discharge from oceangoing vessels, known regionally as "salties," has introduced as many as 180 invasive species to the Great Lakes ecosystem and beyond.