In 2004, the snakehead, a voracious aquatic predator, managed to make its way into the Potomac River, apparently released by an aquarium owner.

For the last two years, the spiderlike Chinese mitten crab has turned up in the Chesapeake and been reported in other places along the East Coast. The crab is suspected of having hitched a ride to the Bay in the ballast tank of a cargo ship.

And last summer, the zebra mussel-famed for wreaking havoc throughout the Great Lakes-was reported for the first time in Pennsylvania's portion of the Susquehanna River. It is believed to have been carried into a reservoir on a recreational boat.

Those are the latest in a string of aquatic invasions that date back to the earliest European settlers. Without aggressive action by states, they are likely to continue, a recent report warns.

But the region's laws and policies to hold back the tide of nonnative fish, plants and animals are highly fragmented, hindering efforts to provide a unified effort in keeping potentially harmful species out of the Bay and its watershed, according to the report, "Halting the Invasion in the Chesapeake Bay," from the Environmental Law Institute.

The report cautions that federal funding and support to lead efforts to combat the invaders "are unlikely to materialize," making state leadership essential. That means states need to go much further in both coordinating existing regulations and in imposing new measures such as regulating ballast discharges from oceangoing ships, requiring the cleaning of recreation boats and limiting the importation and sale of exotic species, the report said.

"There has been an attitude in invasive species management to wait for the federal government to act and then piggyback on that effort," said Read Porter, an attorney with ELI, who wrote the report.That wait has not paid off. Tighter federal regulations on the importation and transport of exotics has moved slowly, and Congress has failed for years to pass invasive species legislation or new laws to regulate the discharge of ballast water from cargo ships entering U.S. waters.

"At this point, I think the states have to take the initiative before it's really too late, before zebra mussels end up in the Chesapeake, which is something that nobody wants to see," Porter said.

Zebra mussels illustrate the type of threat posed by highly invasive species. They were accidentally introduced into the Great Lakes from Europe in the mid-1980s when an oceangoing ship released ballast water, which is kept in giant tanks to stabilize ships at sea.

The mussels have outcompeted native species and are thought to be altering the food web, threatening fish abundance. They multiply so fast that masses of the bivalves clog water intake pipes, jam locks and sink buoys. Beaches covered with dead mussels can be unusable for swimmers. Between 1989 and 1995, control costs were about $70 million a year.

Biologists have long cautioned that efforts to restore the Bay could be dramatically set back by "biological pollution"-the continued introduction of harmful species. Plants such as purple loosestrife and phragmites have already degraded the habitat value of the regions wetlands, while exotic mute swans gobble critical underwater grass beds. The nonnative oyster disease MSX was introduced to the region in the 1950s by a scientist working with nonnative oysters from Japan.

In 2000, about $600 million was spent to control nonnatives, mostly through the U.S. Department of Agriculture to control crop pests. Less than 1 percent of the money was spent to control aquatic plants, fish and diseases.

Because of the potential impacts, and the costs of control, preventing the introduction of an invasive species is considered the most effective and cost-efficient way to head off problems, the report noted.

But right now, the Bay watershed has no regionwide plan to prevent further invasions. Invasive species such as snakeheads, zebra mussels and mitten crabs do not stop at state boundaries, and inconsistent state laws and regulations can actually hinder the ability to prevent the introduction-and spread-of invasives, the report said.

"States and regions facing similar invasive species issues, especially in multijurisdictional ecosystems such as the Chesapeake Bay, can prevent invasions more consistently and effectively by combining efforts under some of their existing laws and regulations," the report said.

To promote regional interaction, the Bay Program in 2005 sponsored the creation of a Mid-Atlantic Panel on Aquatic Nuisance Species. It's one of a number of similar panels across the nation aimed at addressing regional issues and receive small amounts of support from the federal government.

The panel brings together people from state and federal agencies, universities, the private sector and others to work on the problem.

Fredrika Moser, assistant director for research of Maryland Sea Grant, who chairs the panel, said the group has improved communication between the states regarding invasive species and taken some steps to coordinate efforts-it's working on developing a "rapid response" network when new species turn up, for example-but many of the needed actions require efforts by higher-level agency officials. "It's not happening at major decision-making levels," Moser said.

The report agreed, and said a mechanism is needed to ensure issues raised by the panel get addressed by the Bay Program, and ultimately, the states. It also suggested that other interstate organizations, such as river basin commissions that oversee the Susquehanna and Potomac rivers, and the Chesapeake Bay Commission, which represents state legislatures on Bay issues, should be engaged to foster coordinated regional efforts to deal with invasive species.

Among the issues states should address, the report said, are new laws and regulations that combat the major "pathways" that lead to introductions.

For instance, it said the Bay states should adopt strict laws to regulate the discharge of ballast water from commercial vessels. It specifically suggested using Michigan's ballast water law as a model. That law requires oceangoing ships to treat ballast water to kill most of the organisms it contains, and to have a permit from the state before the water is released. Pennsylvania lawmakers are beginning to draft such legislation.

Recreational boaters would not be immune from regulation, either. The report said states should require boat-washing and bilge-pumping for all recreational vessels that are moved from one water body to another-the way zebra mussels are thought to have reached the upper Susquehanna.

Enforcement could be difficult, but the report said relatively inexpensive efforts such as eduction during boat registration, signs and spot checks in high traffic areas could help promote compliance. Even symbolic actions could be important, Porter said. "Development of a model law, even if it was not supported by additional enforcement staff, would bring a little more light to the problem," he said.

The report also said legislation could require that bonds be posted as safeguards by those who wish to import exotic species for sale, aquaculture or other purposes that may lead to their release.

Programs to control invasives typically have little staff or funding-a major problem, according to the report. One way to raise revenue and deter problems is to increase penalties for noncompliance. The report said states should work together, saying "consistent enhanced penalties are needed on a regionwide basis."

Besides new laws, the report said states in the region need to work together to improve consistency among programs. States typically maintain their own lists of problem species, but lists among the states are inconsistent, so states are not focusing limited resources on the same species.

The report said the lists should be "harmonized" and rules adopted so species identified as problems in one state would be added to lists in other states in the watershed unless there was a specific reason not to do so.

It also suggested that states move from so-called "dirty" lists (those that identify problem species) to "clean" lists (those that identify species that have been reviewed and are considered noninvasive).

That change, the report said, switches the burden of proof regarding species listings. With dirty lists, the burden is typically on state programs to demonstrate that a species is a problem. With a clean list, the burden is on those wanting to import species-whether for pet sales, aquaculture or nursery stock-to demonstrate that a species is not a threat if it gets loose.

Other actions are needed to make lists not only consistent, but meaningful, throughout the region. As one example, the report noted, Maryland specifically prohibits the release or introduction of any listed species, but Virginia does not.

"To avoid this situation, states should ensure that their laws include, at a minimum, all of the existing restrictions imposed by their neighbors, unless they have a valid policy justification for an omission," the report said.

The full report is available at the Environmental Law Institute website, www.eli.org