TRAVERSE CITY, Mich. (AP) - Environmentalists sued the federal government Monday over new rules that critics say do too little to prevent cargo ships from dumping invasive species into the nation's waterways. The Environmental Protection Agency is requiring oceangoing vessels to exchange their ballast water, or rinse their ballast tanks if empty, before entering U.S. coastal waters and the Great Lakes. Environmentalists say more extensive treatment of ballast tanks is necessary to keep invasive species from foreign ports from damaging U.S. aquatic ecosystems. Ballast water, which keeps vessels stable in rough seas, is blamed for carrying zebra mussels and many other invasive species into U.S. waters where they have overwhelmed native species and caused other environmental harm. In their lawsuit filed with the 9th U.S. Circuit Court of Appeals in San Francisco, three groups contend the EPA permit's requirements are too weak to meet Clean Water Act standards. "The law does not allow EPA to do what's politically expedient," said Deborah Sivas, director of the Stanford Law School Environmental Clinic. "It requires what is necessary to protect our waters." The clinic is representing Northwest Environmental Advocates, People for Puget Sound and the Center for Biological Diversity. The Natural Resources Defense Council is preparing to file similar litigation in federal court in New York, said Henry Henderson, the group's director of Midwest programs. Benjamin Grumbles, EPA's assistant administrator for water, said: "EPA's vessel permit is a practical and protective step forward for preventing pollution from ships and keeping our waters and coasts clean and healthy." The permit includes rules for 26 types of discharges from ships, such as ballast water, oily bilge water and "gray water" from showers and sinks. It had been scheduled to take effect Dec. 19, but a federal judge in California postponed the date until Feb. 6, giving states more time to impose additional requirements for vessels operating in their waters. EPA previously exempted ballast and most other ship discharges from regulation under the Clean Water Act. Environmental groups and a half-dozen states sued over that policy, and the 9th Circuit ordered EPA to draw up rules for the discharges. The permit requires vessels heading for U.S. ports with full ballast tanks to exchange the water at least 200 miles from shore. Ships with empty ballast tanks must rinse them with salt water to kill freshwater organisms lurking in residual puddles or sediment. But those measures already had been required by Canada and the U.S. Coast Guard. Environmental groups want the EPA to require onboard systems for sterilizing ballast tanks, but the agency agrees with the maritime industry that effective technology remains unavailable. Nina Bell, executive director of Northwest Environmental Advocates, said technology such as filtration and ultraviolet light exposure is far enough along for EPA to have required ballast water treatment. "Shippers have been getting a free ride for decades, polluting our nation's waters with invasive species that clog the intake pipes of drinking water facilities and power plants, harm the commercial fishing industry and destroy habitat," Bell said. Michigan prohibits ships from dumping ballast at its ports unless they have treatment systems. "We know the method used in the EPA permit isn't going to provide protections the Great Lakes will ultimately need," said Robert McCann, spokesman for the state Department of Environmental Quality. California and some states in the Great Lakes region have adopted standards limiting the number of live organisms in discharged water -- a step EPA also did not take.