A U.S. Senate committee has voted to create one national standard for ballast water discharges from commercial ships and prohibit states from imposing tougher requirements.
The bill cleared the Commerce, Science and Transportation Committee on Thursday and heads to the full Senate.
Ballast water keeps ships stable in rough seas. But it often harbors invasive species from other countries that escape when the water is discharged at U.S. ports.
Zebra and quagga mussels are among damaging invaders that have reached the Great Lakes in ballast water.
Shippers favor the bill, saying they could install expensive treatment systems that meet federal standards but still violate state regulations.
Environmental groups say states in the Great Lakes region and elsewhere should be able to exceed federal requirements when necessary to protect their waters.
