The U.S. Border Patrol, Oceanside Harbor Patrol and a helicopter from Customs and Border Protection spotted the boat near Red Beach, south of San Onofre State Beach, the Los Angeles Times reported.
They were arrested Thursday and were being held on smuggling charges. Officials said the boat held 32 bundles of marijuana weighing 741 pounds.
While smugglers still use other methods to bring pot into the United States, smuggling it in via water is getting more frequent. Last year, 867 illegal immigrants and smugglers were arrested along the California coast or at sea, twice as many as in 2009, the report said.
Three smugglers were arrested in June after they were spotted traveling in a boat operating with no running lights near San Onofre State Beach. The boat carried 1,534 pounds of marijuana with a value of about $1 million.
Investigators said smugglers also use waterways to bring illegal immigrants into the United States. Officials said the small boats are often crammed with people, some paying up to $6,000 for their ride.
Last year, two suspected illegal immigrants drowned when their boat, built for 10, capsized near Torrey Pines State Beach. The boat was carrying more than twice the number of passengers for which it was designed.