CLEVELAND, Ohio -- Environmental groups are

that they say could slow down the decades-long, steady march of aquatic invaders into the Great Lakes.

The U.S. EPA on Tuesday agreed to drop its appeal of a lawsuit filed by a dozen environmental groups who had contended that the agency's 2008 permitting rules for the cleaning of ballast tanks was illegal, the groups said.

The advocacy groups, including two from Ohio, contended that the EPA allowed ocean-going vessels to violate the federal Clean Water Act when they dumped their ballast in U.S. waters.

Tuesday's agreement requires EPA to impose more stringent regulations on the ocean-going commercial vessels by 2013. Although the new regulations have yet to be written, they are expected to require ships to meet a high-level of pollution control by killing the organisms.

The goal: keep future invasive species from reaching -- and in some cases fundamentally altering -- vast ecosystems like western Lake Erie, ravaged already by zebra mussels, quagga mussels and round gobies.

Ocean-going vessels crossing the Great Lakes are believed to be responsible for carrying most of the worst invaders into the lakes. Cargo ships often carry millions of gallons of water, often from Europe or Asia, in ballast tanks to help keep vessels upright in rough seas. When they dump the water, the organisms in the water or sediment can establish themselves in another freshwater ecosystem.

"The controls can't go in place fast enough," said Jack Shaner of the Ohio Environmental Council, one of a dozen environmental groups which had sued the agency in 2009, saying the agency's new ballast rules were sorely lacking.

"These destructive, invasive critters respect no boundaries or calendars. The only thing that can stop them is effective technologies and its important we get them in place as soon as possible."

To this point, ships have used a salt water flush, mocked by environmentalists as "swish and spit," to rid ballast of freshwater organisms.

The groups claimed in a lawsuit against the EPA that the agency's 2008 ballast-cleaning rules which allow that technique had violated the 1972 federal Clean Water Act. They said it didn't adequately protect the lakes from the transfer of invasive species.

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"The fact that the federal government had been reluctant to impose regulations has been a huge stumbling block to fighting invasive species," said Eugene Braig, assistant director at Ohio State University's Stone Laboratory on Gibraltar Island in western Lake Erie.

The first confirmed zebra mussel was found in waters near the lab in 1988 and western Lake Erie is considered the bulls-eye for a number of damaging invasives because of its relatively shallow and warm waters in comparison to the other four lakes.

"It's definitely too late for a lot of things -- this should have come much sooner -- but who knows what the next thing down the pike could be," Braig said. "So you can't give up the fight now and anything helps."

Also among the advocates in the lawsuit were the Alliance for the Great Lakes, Natural Resources Defense Council, National Wildlife Federation and various regional or state groups, ranging from the People for Puget Sound in the Northwest to the League of Ohio Sportsmen.

"This settlement puts EPA on track to do the right thing for the Great Lakes," Larry Mitchell, president of the League of Ohio Sportsmen, said in a news release. "The EPA should place limits on ballast water discharges that are strict enough to prevent invasive species from entering our Great Lakes."

One shipping expert, however, said the pending EPA rules might end up as an extra layer over existing international standards, state standards or even upcoming U.S. Coast Guard rules.

"We believe that's because some of protections to this point have already been effective because there hasn't been a new invasive species found in the Great Lakes for four years now," said Steve Fisher, executive director of the American Great Lakes Ports Association.

The U.S. Coast Guard, for example, is about to release new rules that mirror a 2004 international agreement on water quality standards for ballast water dumping.

"I can't see two federal agencies having different standards on how clean is clean when it comes to ballast water," Fisher said. "So unless the EPA goes way out there, this shouldn't affect shippers all that much more because they're already preparing to have to install more expensive technology to treat ballast water."

The settlement also requires EPA to encourage states to develop regionally consistent approaches to setting ballast water standards. Right now, six of eight Great Lakes states, including Ohio, have regulations that reflect the international standard, while New York State has a standard that is far more stringent.