SAVANNAH — Operators of a Savannah-based casino boat routinely allowed patrons to gamble illegally in state waters off Georgia and South Carolina, federal prosecutors said in an indictment that seeks to seize nearly $7 million earned from the casino cruises.

The indictment in U.S. District Court charges the general manager of Diamond Casino and two of his boat captains with operating an illegal gambling business — a charge punishable by up to five years in prison. Filed under seal July 11, the indictment outlining the charges was unsealed by a judge Monday.

“On a regular and routine basis,” the indictment said, the boat’s operators “unlawfully opened and operated the casino aboard the Vessel within the state waters of Georgia and South Carolina.”

To offer gambling legally, casino boats must sail beyond coastal state waters, which extend to 3 miles offshore. The cruise operator’s website says its 184-foot casino boat, the Diamond Royale, had 18 tables for poker, craps, blackjack and roulette wheels as well as 240 slot machines.

Gregory Sicilia, Diamond Casino’s general manager who is charged in the indictment, declined to comment when reached by phone Tuesday. His attorney, Steve Beauvais, did not immediately return a phone message from The Associated Press.

One of the boat captains charged, John Sternberg, also did not immediately return a phone message. A phone number listed for the other captain named in the indictment, Jeffrey Thomas, was no longer working.

Prosecutors said the illegal gambling cruises brought in nearly $7 million between July 2010 and last November, and they say the government is entitled to those proceeds. Prosecutors also want to seize the cruise boat itself.

The indictment came eight months after federal agents served a search warrant on Diamond Casino’s Savannah office in November, seizing laptop computers and documents. Prosecutors said the charges stemmed from an investigation involving federal and state authorities.

James Durham, an assistant U.S. attorney in Savannah, declined to comment further on the case Tuesday. The indictment did not specify whether Diamond Casino operators are accused of staying in state waters for entire gambling cruises or whether they kept casino operations going beyond the time they were sailing in waters where gambling was legal.

Diamond Casino’s office phone has been disconnected. Its website says all cruises have been cancelled “due to remodeling of the boat.”