More than 20 years after the first zebra mussels hitched a ride into the Great Lakes, the United States still doesn't have a requirement to treat ballast water coming into the nation's ports from ships.

Officials with the U.S. Coast Guard are thinking about changing that. The agency has proposed a rule that would require ship owners to install treatment systems to reduce the number of organisms released into the water.

The current proposal calls for an initial phase that would match the International Maritime Organization standard, which has been in place since 2004, limiting the number of organisms allowed in the ballast tanks to 10 per cubic meter. But, beginning in 2012, the Coast Guard is calling for the phase-in of a new standard that would be 1,000 times stricter, allowing for only one organism per 100 cubic meters of water for all ships.

Both environmentalists and shipping companies welcome some form of standard, although they don't agree on how strict it should be, said Cmdr. Gary Croot, chief of the U.S. Coast Guard's environmental standards division. Environmentalists and regulators want the stricter standard to be implemented right away, while shipping companies would like more time.

Dealing with ballast water has been a murky issue since 1972, when it was initially regulated, then exempted, by the Clean Water Act.

Ocean-going cargo ships typically draw in water while in ports to stabilize their vessels at sea, then let out the water when they arrive at their destination. During the long journey, many of the organisms living in the ballast tank die. But hardy invaders live on, and they bring reproducing populations into new bodies of water that can devastate native species.

Zebra mussels came to the Great Lakes in the mid-1980s in ballast water, and proved they could wreak havoc on water supplies. Now, they're established in 23 states, including California. San Francisco Bay is filled with non-natives that have come in through ballast water.

The Chesapeake has had its own struggles. More than 3 billion gallons of ballast water are released into the Bay each year, as much or more than any bay in the nation.

The furry Chinese mitten crab likely came here courtesy of ballast water, as did the rapa whelk, an aggressive sea snail that eats clams and oysters. Zebra mussels were found last year in the uppermost reaches of the Chesapeake Bay, at the mouth of the Susquehanna River.

Scientists at the Smithsonian Environmental Research Center in Edgewater, MD, have identified more than 170 nonnative species that have established self-sustaining populations in the Bay, many of which are believed to have arrived in ballast water. Because of such concerns, a Bay Program task force in 2001 issued a report that called for federal action to regulate ballast water.

"This is not a regional issue, not a national issue. It's a continental issue," said Jeff Alexander, a media consultant with the National Wildlife Federation who wrote a book about invasive species in the Great Lakes. Alexander has long been critical of the Coast Guard for failing to regulate ballast water.

Shipping companies have been waiting for the Coast Guard to impose some kind of standard before investing in ballast water treatment systems, which can get out many of the unwanted organisms but can cost as much as $1 million per ship.

"We acknowledge that aquatic invasive species is a very difficult problem, a tragedy in the Great Lakes, and we know we are partly responsible for it," said Marc Gagnon, government affairs director for Fednav Limited, a large shipping company.

Treatment systems on board would nearly eliminate the problem. But, he added, "Companies are not going to invest in shipping systems, if they don't know what they have to treat."

In 1996, Congress passed the National Invasive Species Act, mandating a national program to regulate ballast water. But, Groot said, Congress required the program to first be voluntary, and then be phased in.

By 2004, the Coast Guard did require ships to flush ballast water from their tanks and replace it with ocean water when they were at least 200 miles from shore-the idea being that organisms living in salty ocean water were unlikely to survive when released in fresh or brackish ports. But most of the ships couldn't comply with that standard.

"Based on the records we have, almost a third can't safely conduct a ballast water exchange at all, and 60 percent can't do it 200 miles from land," Groot said.

In the absence of a strict Coast Guard standard, several states took matters into their own hands. In 2000, Washington state required ships to exchange their ballast water 50 miles from shore. Oregon and California soon followed suit.

Under the proposed rule, the Coast Guard would require treatment systems that would be more effective than just ballast water exchanges at removing unwanted organisms. The Coast Guard plan is for the final rule to become effective by 2012, when new ships will have to follow the stricter standard. Older ships weighing between 5,000 and 15,000 metric tons will have until 2014 to be retrofitted. All ships will need to follow the stricter standard by 2016.

Allan Pleus, aquatic invasive species coordinator with the Washington Department of Fish and Wildlife, said his state's stricter standard "absolutely helps" in keeping coastal invaders out of the Puget Sound.

Pleus said he'd like to see the Coast Guard move right to the stricter standard, instead of phasing it in.

"There's been a lot of opportunities on a lot of different sides. And yeah, we would like to see things done faster," he said.

Last year, the EPA began requiring permits for ships that discharge ballast water after losing a lawsuit in California on the matter. But those permits do not look at the number of organisms in the water.

In Baltimore, the 2-year-old Marine Environmental Resource Center, which is part of the University of Maryland Center for Environmental Science, is helping ships test their ballast through a partnership with the Maryland Port Administration.

Center marine biologist Mario Tamburri, who has been working on ballast water issues for 10 years, said the Coast Guard's approach is reasonable.

"They're pretty strict to start with, and it's smart to have a goal to get better in the future," he said. "Phase 2 is just not possible right away."

The comment period for this rule ends Dec. 4. For information, see