The U.S. Coast Guard and the EPA are hoping to soon have in place a new standard for ballast water.

The two agencies have been working on a standard since 2009, when they announced that they would like to introduce a standard that is 1,000 times more strict than the current one.

The International Maritime Organization Standard, which has been in place since 2004 as a guideline, limits the number of organisms in a tank to 10 per cubic meter of water. The proposed standard allows only one organism in 100 cubic meters of water. The agencies had planned to make the IMO standard mandatory and phase in the stricter standard.

Since 2004, the U.S. government has only required ballast water exchanges, not an organism limit, to reduce the number of aquatic invasive species coming into the country. But ballast water exchanges have their limits - not every ship can do them safely, and they do not remove all of the organisms in the tanks. A far better way to manage invasives, the agencies reasoned, was to get ships to build treatment systems onboard and treat the problem during the journey.

"We have always looked at exchange as a stopgap measure," said John Morris, the Coast Guard's project manager for ballast water regulations. "At some point in the future, our proposed regulations will replace exchange as an option."

While some ballast water treatment systems can meet the IMO standard, none can yet meet the proposed more stringent standard, which the agencies had hoped to phase in by 2012. Environmentalists, scientists and shipping companies are worried about instituting a standard that cannot yet be met.

"We're looking at systems we haven't even dreamed up yet," said Mario Tamburri, a biologist with the Marine Environmental Research Center at the Baltimore Inner Harbor. "IMO is achievable. Anything beyond that is not."

Tamburri's lab is housed on a military ship in Port Covington, but it is moving to a barge this fall. On the ship, his team tested six systems to determine how well they removed organisms from the water. Tamburri also served on the EPA Science Advisory Board's ballast water panel.

The ballast water standard is necessary because each of the 26 states with maritime shipping industries have different standards for dealing with ballast water. New York's is one of the strictest, but Washington state has put in some stringent measures, too, hoping to keep aquatic invaders from the coast of California at bay. Canada also follows different rules.

The two agencies have received more than 2,000 comments on the proposed standard, Morris said. Many of them have come from industry, which is seeking some certainty on what the standard will be before making multimillion-dollar investments in ship upgrades, and from environmentalists who worry the standards aren't going to be strict enough or come soon enough. Some scientists worry the years-long delay in establishing a standard has allowed more organisms to enter U.S. waterways.

"I know there are ships that have been built that would have had systems on board, if they knew what the rules were," Tamburri said. "And we have missed the chance to treat that water."

Ballast water from ships has brought hundreds of new species to the shores of the United States. Some are harmless; others have disrupted the food web and civil infrastructure.

Zebra mussels have crowded out other species since their arrival in the Great Lakes more than two decades ago, and they have fouled pipes and caused billions of dollars in damages.

The Great Lakes also have to contend with the rapidly reproducing round goby, a fish with no natural predators there, as well as the parasitic sea lamprey.

The Chesapeake contends with the Chinese mitten crab and the rapa whelk, a predatory snail from the Black Sea that feasts on native oysters. Ballast water also carries disease-bearing phytoplankton, and can bring in marine epidemics such as vibrio cholera and enterococci bacteria.

Invasive species are "a real problem. And we will be the first to recognize it," said Marc Gagnon, director of government affairs for Fednav, a Montreal-based maritime company. Many of the measures that governments and companies have put in place since 2006 have slowed the arrival of invasive species, he said. And, he added, his company is ready to put treatment systems on board, as soon as they know what the rules are. Fednav, he said, is "waiting impatiently."

Bruce Bowie, president of the Canadian Shipowners Association, is worried that the delay in putting together a standard, or the possibility that it won't be achievable, will persuade some shippers to seek other means of transit. Those, he said, will be less environmentally friendly.

The courts have played a role in ballast water management, too. In 1999, environmentalists sued the EPA for failing to regulate ballast water as a point source. A judge ruled in 2008 that the agency had to do so, thus giving the regulation responsibility to both the Coast Guard and the EPA.

In the meantime, several states, frustrated with the process, took matters into their own hands, creating ballast water restrictions that are more strict than federal guidelines.

The shipping industry has filed a lawsuit in New York over that state's strict ballast water regulations. The state requires ships to treat ballast water to stem any new invasions. That means any ship coming into New York must have a system on board, even though the federal government and other states don't require it. In other states, the courts have upheld the states' rights to have a standard that is more strict than the EPA's or the Coast Guard's.

Morris said that, even when the agencies do put a new and stricter standard in place, the states will still have that right.

"There are going to be vessels that visit a number of different state waters, and they're going to encounter different organism limits and chlorine limits," he said. "It's very complicated for the regulated industry."