An unexpected surge in visitors this weekend caught many Vineyard business owners — and public health officials — by surprise as people jammed downtown streets and open-air restaurants from Friday to Sunday.

Open-air restaurants were unexpectedly swamped. — Ray Ewing

Previously empty harbors filled with boats and newly opened restaurants filled with patrons — prompting new concerns about social distancing as an unprecedented summer season on the Island gets under way.

Crowds of people, many not wearing masks, were seen throughout the weekend traversing downtown Main streets and packing Island harbors, creating a festive atmosphere but raising public health concerns and some alarm among a handful of swamped restaurateurs.

Oak Bluffs harbor master Todd Alexander said Saturday was the busiest day of the weekend — and the summer so far.

“We were pretty much sold out,” Mr. Alexander said. “It was pretty much like every weekend [in the past].”

The Steamship Authority, which has been reporting dismal passenger numbers throughout the spring and early summer, saw a large uptick in traffic as well. Spokesman Sean Driscoll said passenger traffic was up about 25 per cent over recent weekends. Although passenger numbers are still running at about half their normal volume, Mr. Driscoll said cars traveling on ferries were “pretty much running full.”

The opening of restaurants to outdoor dining — combined with warm, summery weather — led to the surprising crowds, some officials speculated.

Mr. Alexander said Saturday felt like the first true summer day in the harbor.

“I think what people are focusing on is what people do when they come on shore,” he said. “And I don’t really have an answer for that.”

In Edgartown, Scott Hannah, general manager of the Seafood Shanty, said the restaurant reached its limited outdoor capacity for most of the weekend. He said the crowd largely resembled patrons from past summers, including golfers down for the weekend, seasonal residents and bachelorette parties.

Boaters at Church's Pier on a sold-out weekend in the Oak Bluffs harbor. — Ray Ewing

“We were as full as we could have been,” Mr. Hannah said.

Health officials and business owners on the Island expressed both surprise and dismay at the crowds, saying that social distancing protocols were flouted and that more had to be done to abide by regulations. Photos and videos of the Oak Bluffs harbor, circulated widely on social media and local news outlets, showed large crowds with few people wearing masks.

“Numbers-wise, it was pretty insane,” said Doug Abdelnour, a businessman who owns Nancy’s on the Oak Bluffs harbor. “None of us were prepared for that.”

Tisbury health agent Maura Valley said the boards of health had seen the videos of the harbor as well.

“That was pretty horrifying this weekend,” Ms. Valley said. “We were all kind of surprised at the numbers we saw of the people not wearing masks.”

As the state gradually reopens in phases, allowing restaurants to provide outdoor dining and lodging services to book guests, business owners on the Island find themselves navigating an altered summer landscape. While the handful of outdoor restaurants on the Oak Bluffs harbor — including Nancy’s, Lobsterville, The Sandbar and Coop De Ville — were all open for business and bustling this weekend, limits on capacity and indoor dining along Circuit avenue eateries meant that large crowds were confined to small spaces along the waterfront.

Passenger ferries, including the Island Queen, also service the harbor and provided many of Nancy’s customers over the weekend, including large numbers of college students from the Cape, Mr. Abdelnour said. And for the first time this year, the Hy-Line, a passenger ferry from Hyannis, ran trips through Oak Bluffs as well.

Downtown Edgartown saw busy weekend too. — Mark Alan Lovewell

“I expected people to be more hesitant and trickle out slowly, but that’s definitely not what happened,” Mr. Abdelnour said. “We did what we were supposed to do, and we did our best to do it in a safe way . . . but it is so difficult to manage from last weekend to now.”

While Mr. Abdelnour said he was chagrined he had not anticipated the large crowds, he added that it was challenging to handle social-distancing protocols with an already limited staff. He said his tables are appropriately distanced, and he hoped the state would soon allow more capacity for indoor dining so the pressure doesn’t fall on the few outdoor restaurants to service large crowds. He felt opening more restaurants was the only adequate solution.

“Putting it on three or four restaurants, and then being mad at them for trying to supply what customers want, is just making it worse,” Mr. Abdelnour said. “If we were to limit our capacity more, the line just goes further down the harbor.”

Ms. Valley said the boards of health were having conversations about how to handle the large crowds on town land and were aware of the problem. Although she did not have specific solutions to how the crowds would be dealt with, she said more public signs about masks being required was a first step.

“We all saw the pictures in Oak Bluffs this weekend, and that can’t continue,” Ms. Valley said. “We need to figure out a way to regulate it. We need to get more signage. We need to make people more aware of the fact that this is going to be enforced.”