In a crackdown designed to avoid a repeat of last July Fourth, when 4,000 people descended on a Nantucket beach, police arrested 49 people on the island Wednesday, Nantucket Police Lieutenant Jerry Adams said.

Authorities have arrested 65 people on the island since Monday, Adams said.

The most common offenses were open-container violations, underage drinking, and disorderly conduct. Police have also cited partiers for possessing fake IDs, littering, and urinating in public, he said.

The aggressive enforcement effort, complete with beach checkpoints, helped rein in rowdiness this year, Adams said.

“I think it went very well,” Adams said. “We managed to keep the situation under control under the circumstances.”

Most of those arrested were in their 20s or late teens, and the majority were not permanent Nantucket residents, he said.

Last July Fourth’s partying, which primarily took place on Nobadeer Beach, left multiple people with alcohol poisoning, including one who nearly died, Adams said.

This year only a couple of the patients seen by Nantucket Cottage Hospital needed treatment for alcohol-related health issues, and none were in life-or-death conditions, said hospital spokesman Bill Ferrall.

The hospital’s emergency room still saw 64 patients Wednesday, up from 58 last July Fourth, but the total number of patients between July 1 and July 4 decreased slightly this year, Ferrall said.

On Sept. 4, by comparison, the emergency room saw an average of 30 patients over the past two years.

Roughly 50,000 visitors pack the island during the summer, up from a year-round population of under 11,000, said Nantucket Town Manager Libby Gibson.

Those arrested this week represent only a fraction of the people celebrating July Fourth, Gibson said. She said police efforts helped ensure a positive holiday for the most people possible.

“We need to make the island safe for people and enjoyable for everybody, which includes not only people going to the beach but [also] neighboring property owners,” she said.

Gibson said feedback from residents has been mixed. Some told her the police presence was too large, others said it was too small, and some said it was appropriate.

“Maybe if we get all three, we’ve done OK,” she said.

Nantucket officials began planning this year’s enforcement strategy shortly after last July Fourth.

The plan included the circulation of fliers that urged partiers to act responsibly. One showed the inside of an ambulance, asking in bold letters: “Is this your idea of a good time?”

As part of the strategy, Nantucket Police deployed 20 more officers than they do on a normal shift, Adams said. The State Police, the Barnstable County Sheriff’s Office, and the Nantucket County Sheriff’s Office also sent reinforcements.

In a shift from last year, most of this year’s partying took place on a beach called 40th Pole.

While partying has intensified in recent years, with last year’s debauchery described as the most raucous of any in recent memory, the phenomenon is not new on the island.

Maureen Beck, who retired earlier this year as chair of Nantucket’s Beach Management Advisory Committee, remembered one year in the 1970s when Plymouth Police sent down an equestrian unit to assist in enforcement.

The holiday revelry, however, does not reflect the general experience of Nantucket residents, she said.

“What we’re trying to do here is stop the orgy and bring on the happiness and peace of being here,” Beck said.

Martha’s Vineyard had similar partying issues in the mid-1990s, recalled Lieutenant Tim Williamson of the Oak Bluffs Police Department, one of six local departments on the island.

But a few years of aggressive police work helped change the environment, and this year the Oak Bluffs police did not arrest anyone on July Fourth.

Williamson said he expects the efforts of Nantucket officials will ultimately yield similar results.

“I think that eventually the partygoers will get the message,” he said.