Superintendent Phyllis Green said Monday her emergency order was designed to prevent water contaminated with a fish-killing virus from being dumped near the island, home to 12 types of trout including the rare coaster brook trout.

Viral hemorrhagic septicemia, or VHS, is among many exotic species that scientists believe have been scooped into ships' ballast tanks in foreign ports, then discharged into the Great Lakes.

"The entire lake fishery is threatened by this virus," Green said. "We need to do everything we possibly can to stop it."

A shipping industry spokesman said the order would have little practical effect.

It would not prevent infected fish from migrating to the island on their own if the virus gets into Lake Superior, said Glen Nekvasil, spokesman for Cleveland-based Lake Carriers Association.

VHS has caused large fish kills in the other Great Lakes and some inland waterways but has not been spotted in Superior.

Freighters usually discharge ballast in port, not the open lakes, so it's unlikely they would release VHS around Isle Royale anyway, Nekvasil said.

"Everybody wants a solution to this problem but you have to look at realities," he said.

Green, however, said cargo vessels occasionally deposit some of their ballast within the park's jurisdiction on their way to Thunder Bay, Ontario, about 40 miles farther north.

If nothing else, she said, the restriction may slow the spread of VHS toward Isle Royale while encouraging the shipping industry to quicken development of ballast cleansing technology.

The policy takes effect Tuesday and covers 475 square miles of water, including an 8-mile slice of the shipping lane used by vessels heading northward and 12 miles of the southbound corridor.

Federal law empowers national park superintendents to impose regulations for protection of natural resources, Green said, adding that her supervisors had approved the order. It is a temporary measure until a permanent rule can be adopted.

The U.S. Coast Guard requires ships to keep logs of their ballast discharges. Isle Royale officials will use those documents to monitor compliance with their policy, Green said. They may also consult records kept by state agencies such as the Michigan Department of Environmental Quality, which issues ballast permits.

Each violation is punishable by a $5,000 fine.

The order will apply mostly to Canadian vessels and oceangoing ships from other countries. U.S.-flagged freighters on the Great Lakes seldom call at Thunder Bay and enter Isle Royale's boundaries only when bad weather forces them to use a northerly route, Nekvasil said.

The Isle Royale order reflects widespread frustration with the absence of a federal policy on ballast treatment, Nekvasil said.

"Everybody is kind of going their own way," he said, noting that Michigan has enacted its own ballast water law and several other Great Lakes states may do so. "We're going to end up with this hodgepodge of regulations, some of which may be conflicting."

The industry says it is making progress on ballast technology but needs more time.

Green said effective treatments already exist. She said Isle Royale would begin using chlorine to sterilize ballast tanks on its 165-foot ship, Ranger III, which hauls passengers and cargo between the island park and Houghton, Mich., 73 miles to the southeast on the Upper Peninsula mainland.

The ship's engineers and university researchers devised the method, which meets federal clean-water standards, she said.

"For under $600, I can kill everything in those tanks and I can neutralize the chlorine with vitamin C," Green said.