Amid the busy Memorial Day weekend boat traffic on the Miami River, sharp-eyed Customs and Border Protection marine agents spotted one cruising vessel whose name -- High On the Hog -- they had reason to recognize.

As they stopped and searched the 42-foot Sea Ray near the 12th Avenue Bridge, one of the two crew members jumped in the river and swam away. When the agents looked below deck, they knew why: 30 people were crammed in there, all would-be illegal immigrants. Right off downtown Miami in the middle of a Saturday afternoon.

Even more surprising: All but two were Jamaican, and 17 of those had previously been deported from the United States for having criminal records, agency officials said Wednesday. The other two passengers were from the Dominican Republic.

The first crewman got away. The other, identified only as a Cuban national residing in the United States, was arrested on suspicion of migrant smuggling, said Customs and Border Protection Special Agent Zachary Mann, an agency spokesman. The passengers were being held for questioning by Immigration and Customs Enforcement agents and are subject to deportation.

Beyond conceding that it was unusual to discover so many Jamaicans attempting illegal entry at once, especially so many previous deportees, Mann was mum on other details, citing an ongoing investigation. The agency did not announce the interdiction for five days.

''It's a significant find,'' Mann said.

It was not entirely coincidental, however. Mann said they picked out the High on the Hog because of an ongoing investigation but he would not elaborate.

''We saw the name and wanted to take a closer look,'' Mann said.

The interdiction comes amid a far-ranging U.S. crackdown in South Florida on the smuggling of illegal aliens from the Caribbean, predominantly from Cuba. Just last week, federal prosecutors charged 26 South Florida suspects with conspiring to smuggle in 225 Cuban migrants in 12 different boat trips. In the preceding month, indictments were also unveiled against 41 other men suspected of smuggling in some 400 Cubans in 20 separate operations.

Saturday's operation may be a lesser-known variation on the usual pattern.

Mann said he did not know where the boat picked up its passengers. But Bahamian immigration authorities have said they suspect Jamaicans deported from the United States are using the islands as a stepping stone for illegal re-entry into the country.

In January, U.S. immigration authorities deported a notorious Jamaican gang leader who had re-entered the country after being kicked out in 2006. Re-entry after deportation is a felony.

Saturday's brazen attempt to smuggle people down the river in broad daylight is not unprecedented. Smugglers sometimes use the cover of busy boating holidays to attempt entry, Mann said, thinking federal officers are not working.

Such attempts, once more common, have been relatively rare in recent years, however. The last to be discovered may have been in 1998, when a decrepit wooden boat disgorged 150 Haitian immigrants on a weekday afternoon on the river near downtown Miami.

In the early 1990s, following the ouster of Haitian President Jean-Bertrand Aristide, there were a number of interceptions:

In November 1992, about 70 Haitians jumped from a freighter at the old Dupont Plaza hotel on the Miami River downtown and fled in waiting vans. A month later, 117 Haitians were found crammed into the hold of a 70-foot freighter that ran aground off the Port of Miami.

A month after that, the Coast Guard stopped a freighter carrying 351 Haitians at the Port of Miami.