LOS ANGELES — New federal regulations will bar cruise vessels and large commercial ships from discharging sewage within three miles of California’s coastline, the U.S. Environmental Protection Agency announced on Wednesday.

Officials say the new rules, which take effect next year, will amount to the nation’s largest ban on sewage discharge and will keep roughly 20 million gallons of sewage out of coastal waters annually.

A 2005 state law bans ships from dumping hazardous substances and runoff from showers or sinks, but regulating sewage falls under federal jurisdiction. The federal ban, which applies to ships that weigh more than 300 tons, will give the U.S. Coast Guard the authority to cite vessels for violations.

“”We now have the benefit of a rigorous state law and federal enforcement,”” said State Sen. Joe Simitian, a Democrat, who wrote the California law and asked the EPA to establish the sewage discharge ban in 2006.

Simitian said the sewage ban will go far to keep cruise ships, which he called “”floating cities,”” from contaminating coastal waters. “”Ask yourself whether you’d like to have a community of three or four thousand people dumping their waste on your doorstep,”” he said.

But the nation’s largest association of cruise lines said on Wednesday that the ban won’t affect its vessels because the ships already follow a non-discharge policy as stringent as the federal ban.

“”It will have no impact on our members,”” said Michael Crye, of the Cruise Line International Association.

Crye said major cruise lines operating off the coast of California have not discharged sewage within three miles of the coast ever since the state passed the coast contamination law in 2005. Instead, he said, ships store the sewage in large holding tanks until it is discharged at municipal wastewater treatment facilities or eventually emptied off-shore.

California currently has nine small no-discharge zones. Under the Clean Water Act, states may ask the EPA to establish no-discharge zones to protect and restore water quality.

The EPA’s announcement is the latest in the effort to regulate the $40-billion cruise industry. Last month, President Barack Obama signed a law that mandates reporting of crimes at sea, improves ship safety and requires ship staff training on collecting assault evidence.