WASHINGTON — Ship operators would face new controls on discharges of ballast water as a way to lessen the threat of invasive species under a bill a Senate panel approved last week on a voice vote.

Environmental groups, state officials and lawmakers, while wanting stronger controls on ballast water, are opposing the bill's provisions that would exempt the discharges from the Clean Water Act and pre-empt states' ability to enforce their own anti-pollution laws.

"The bill has some good provisions," said Corry Westbrook, legislative director for the National Wildlife Federation. "But I don't know what is going to happen until they (senators) can find a compromise."

Ships take on ballast water for stability and often discharge it in ports as cargo is unloaded. It has been blamed for transfer of some invasive species, such as snowflake coral in Hawai'i and the zebra mussel in the Great Lakes, that can cause havoc with local environments and economies.

Sen. Daniel K. Inouye, D-Hawai'i, chairman of the Senate Commerce Committee, said the bill strengthens federal authority over ballast water discharges to help control invasive species from entering U.S. waters.

"The committee's approach is a pragmatic, bipartisan approach that offers the opportunity for meaningful and effective environmental legislation to move through the Senate and ultimately reach the president's desk," said Inouye, who first introduced ballast water legislation in 2005.

The bill would create a ballast water management program for invasive species that includes national standards for treating the water and calls for the Coast Guard to implement the program.

The bill would require treatment technology that is 100 times stronger than minimum international standards on all vessels calling at U.S. ports. But until the technology is available and cost-effective, ships still would be allowed to exchange ballast water with water in mid-ocean.

During the committee discussions, Sen. Barbara Boxer, D-Calif., said she was not happy with the bill because of the Clean Water Act exemption and other problems. She won agreement from Inouye for continued work on the bill before it comes up for a full Senate vote.

"The bill, as drafted, is a direct attack on the Clean Water Act," she said.

The attorneys general of six Great Lakes states and the head of the Oregon Department of Environmental Quality also sent letters to the committee complaining about the Clean Water Act exemption and the pre-emption of state laws.

The attorneys general said in a letter that the state law pre-emption was contrary to the bedrock environmental law principle that states may set standards more protective of their citizens' environmental health and safety than those set by the federal government.

Stephanie Hallock, director of the Oregon Environmental Quality Department, wrote that the pre-emption of state authority "strikes us as ill-advised and the states usually understand the local resource conditions and the appropriate methods of protection."

"It is hard to believe, for example, that the waters and conditions of Oregon and Florida are so similar that a single, 'one-size-fits-all' approach is practical or effective," she said.

Reach Dennis Camire at dcamire@gns.gannett.com.