STONY BROOK - Federal and state lawmakers announced today that a 760- mile stretch of the Long Island Sound has been designated a "no-discharge zone," making it illegal to dump raw sewage into the water. The measure, which goes into effect Thursday, will require boaters to go to special pump stations to dispose of their sewage.Environmentalists say the no-dumping regulation is a cause to celebrate. "It's good news for boaters, it's good news for beachgoers, good news for everybody," says Adrienne Esposito, of the Citizens Campaign for the Environment. The state Department of Environmental Conservation will be in charge of enforcing the new law.