HIGH BRIDGE, N.J. — Lake Solitude, it was not.

For years, the 35-acre picturesque lake, waterfall and century-old dam had been an unspoiled treasure for local residents, but through the power of social media, the secret got out.

People began pouring in, bringing portable speakers, children and food, and leaving behind trash. Borough officials installed extra garbage cans and portable toilets, and brought in police officers to direct traffic — many vehicles with New York license plates. On a recent Sunday, some visitors had to be turned away.

Residents had seen enough. They swarmed a virtual town-hall-style meeting this month, demanding that Lake Solitude be shut. Last week, the Borough of High Bridge complied, closing the area to all visitors.

Some of the complaints stemmed from fears that visitors might bring the coronavirus from New York City, about 50 miles east of the borough. But some of them focused bluntly on ethnicity.

High Bridge is nearly 95 percent white, but the lake attracts a much more diverse group.

On the last weekend that Lake Solitude was open, mothers and fathers were paddling with toddlers underneath the waterfall’s spray, grandmothers were basking with their feet in the bucolic river and 20-somethings were taking drone photos with the imposing dam.

“We have droves of out-of-state Spanish people and they leave their crap lying on the ground,” said Lester Tomson, 58, who regularly fished the stream.

Mr. Tomson, a registered Democrat, is one of a number of people who, on social media and in conversation, have suggested that Immigration and Customs Enforcement should have been called to the park.

“It’s not a racist thing,” he said in an interview. “It’s a thing where you observe things, and your observations are based in facts and not in racism.”

Lake Solitude is one of several normally quiet oases for locals that have been recently overrun by day trippers from New York City — where public beaches and pools were mostly closed until this month — who are looking for closer places to visit because of the pandemic.

In Woodstock, N.Y., about two hours north of Manhattan, town officials said they had to shut their popular Big Deep and Little Deep swimming holes because of the “littering and messes left behind by visitors” that made it difficult to “maintain safety during the pandemic.”

Elsewhere in the Catskills, more than 300 people attended a town-hall-style meeting held outdoors last week to complain about the traffic and trash brought by outsiders at Kaaterskill Falls, especially at its popular swimming holes, Fawns Leap and Dog Hole.

Greene County, home to Kaaterskill Falls, is over 96 percent white. But Daryl Legg, the town supervisor of Hunter, where the falls are, rejected the idea that race had any part to play in the complaints.

“People come here for the scenery and beauty of the place,” he said, “but leave red Solo cups at the bottom of the swim hole, and people defecate and pee in the woods and it smells like a latrine after Woodstock.”

But the tensions have been especially sharp in New Jersey, where state officials in April gave municipalities broad discretion to close public parks as a way of curbing the coronavirus.

In Ocean County, borough officials in Lakehurst cited overcrowding in their decision to shut Lake Horicon to visitors in May, a day after the state had reopened county and state parks. In Long Branch, in Monmouth County, the police temporarily blocked beach access this month after a deluge of beachgoers made social distancing impossible.

In High Bridge, the decision last week to close Lake Solitude was made for health precautions and because the parking lots were at capacity, according to the borough’s mayor, Michele Lee.

But three days earlier, during the virtual meeting, some public comments cited other reasons: One man expressed that he felt unsafe after a male visitor to the lake said, “Hola, señorita,” to his wife.

“We are an inclusive community; We are going to be accepting of everybody, regardless of race or faith or who you love,” Mayor Lee, a Democrat, said. “We did what we have to do because it was really becoming a safety concern.”

The mayor said that the crowds grew drastically after a TikTok video that called the site a “hidden gem” went viral.

Ms. Lee said that the borough’s decision had nothing to do with any overt or subtle xenophobia or racism — like the discussions about the cleanliness of “those people” that could recently be overheard over pints of Keepin’ Local beer on the patio of a local brewery and taproom.

“I find those kinds of comments more disgusting than any of the garbage I saw left behind at the lake,” Mayor Lee said.

At Lake Solitude the day before it was shut, the ground was pristine, and few people enjoying the park felt there was a problem.

“People are just looking for an excuse not to have colored people around, to get us out of their town,” said Alej Rodriguez, 26, a truck driver who drove in from Upper Manhattan with his family, to visit the lake and the sights on the rolling grounds, like the remains of the Union Iron Works forge, which smelted cannonballs for the Revolutionary War.

“You’ve always got a target on your back as a colored person,” he said. “You’ve always got to watch your back, even at a beautiful lake where we come to have fun.”

Not far from Mr. Rodriguez, a man, who identified himself as a High Bridge resident but would give only his first name, Mike, was taking photos of people swimming with a long range lens.

“I’m documenting the problem,” said the man, who was white, explaining he was angry that the bathers were not wearing masks as they swam, and worried that the people playing in the water were contaminating it.

Edward Bielcik, 74, had heard talk of the overcrowding and wanted to see for himself, he said. He was one of several residents strolling the park with cameras to document the claims. “They said the Latin Kings tagged the area,” Mr. Bielcik said.

For several weeks, Mayor Lee, a financial adviser who does not take a salary for her borough position, had pushed to keep the park open, under her belief the newcomers could help make High Bridge a tourist destination. “If we get this right, it’s a great situation for the town,” she said.

Plans are underway to figure out how to reopen and accommodate any crowds, the mayor said, but there is no timeline yet to do so.

Some of the borough’s residents say they can’t help but feel that uglier impulses are behind the desire to close the lake.

At Scout’s Coffee Bar & Mercantile on Main Street, the owner’s eyes filled with tears when she recounted the words used about the visitors that she had overheard at her barista’s counter. Just a month before, a Black Lives Matter rally had taken place down the street.

“We just went through all the protests, and we are all learning about how we can be better allies to people of color, and this is our opportunity. It’s disheartening,” said the owner, Nicole Poko, 38, who is white. “It just feels like there is a lot of work to be done.”