A new rule for oceangoing vessels entering the Great Lakes could help block the introduction of new invaders like those that have already caused a biological and economic plague for the states and provinces that share the lakes.

Under the rule, the ships, called salties, will have to swish saltwater through their ballast tanks and pump it back into the ocean 200 nautical miles offshore. Biologists believe the saltwater will kill most freshwater animals and plants living in the tanks.

Critters like zebra and quagga mussels native to the Black Sea and dumped in the Great Lakes from ballast are responsible for an estimated $5 billion a year in damage.

The mussels cover municipal water intake pipes and have spawned a type of botulism that has led to massive bird die-offs on Lake Michigan. Communities spend millions to clean the mussels from their pipes. The mussels also have changed the ecosystem of waters like Lake St. Clair, making them much clearer by filtering out the plankton they eat.

Other ballast invaders have been tied to fish viruses such as viral hemorrhagic septicemia, which has led to large fish die-offs. Fish accidentally planted in the Great Lakes have outcompeted existing species for food and hurt fishing-related tourism.

Scientists say 70% of the invaders that have arrived in the Great Lakes since 1959, when the St. Lawrence Seaway opened the lakes to international ship traffic, have come from the salties' ballast water.

The rule takes effect in late March, when ship traffic resumes.

The rule, proposed by the St. Lawrence Seaway Development Corp., part of the U.S. Department of Transportation, will require more inspections of ships' tanks. Violators could be fined up to $36,625 per incident.

"Ballast water is the most important way these species get into the lakes, and this new rule will be very helpful," said Hugh McIsaac, a researcher at the University of Windsor. McIsaac said a study he and others did last year showed that flushing tanks with saltwater killed 95% to 99% of foreign organisms in the tanks.

"This is a step we wish they had taken some time ago," said Bob McCann, spokesman for the Michigan Department of Environmental Quality.

Ships carry ballast for stability. If they enter the lakes filled with cargo to unload at ports, their ballast tanks are empty. If they come without cargo, their tanks are full.

Those carrying ballast have been required since 1993 to refill their ballast tanks with salty water in the deep ocean, ensuring that organisms that might linger in their tanks would be killed.

But up to 90% of the ships entering the lakes don't have ballast in their tanks and have not been required to flush their tanks. Even though the tanks aren't full, they have leftover sediment and small amounts of water in which organisms can live.

When they unload their payloads and open ballast tanks in port to take on water, the organisms can escape into the Great Lakes and create havoc.

"That loophole has been a significant issue," said Ken DeBeaussaert, director of the DEQ's Office of the Great Lakes.

The same rule has been required in Canada since 2006, said Terry Johnson Jr., administrator of the St. Lawrence Seaway Development Corp. Johnson said the shipping industry has agreed to the rule, which was published in the Federal Register Dec. 31.

Since the federal government failed to act, Michigan adopted its own law a year ago requiring ships to get permits proving they'd sterilized their tanks before dumping water in Michigan ports.

"We knew it wouldn't solve the problem, but we decided we had to start somewhere," McCann said. All eight Great Lakes governors sent a letter last July to Congress, urging federal action. Environmental groups pledged lawsuits or a moratorium on salties entering the lakes.

But nearly everyone said the saltwater flushing won't stop all invasive species.

Johnson said it's an interim measure until Congress acts on pending legislation, which would require more high-tech methods to sterilize tanks than saltwater.

The shipping industry has lobbied against the legislation, saying it's too costly.

"I'm glad they've done this, but we still need a comprehensive solution that will close the door on invasives once and for all," said McCann.

Contact TINA LAM at 313-222-6421 or tlam@freepress.com.