There has been confusion after police asked beach-goers at Helen's Bay to leave the area on Sunday, citing Covid-19 regulations.
Swimmers were using the popular County Down spot when officers arrived and asked them to disperse.
One man had been finishing a "mile a day" swimming challenge raising money for charity.
No fines were issued by police officers but they said they would "not shy away from enforcement when it is necessary".
Police said that they believed a large number of people had gathered to watch the charity swimming event.
'Ikea or Tesco'
However, a local businessman who was swimming at the beach said he was "absolutely baffled" by the police's approach.
Gareth Murphy told BBC News NI: "I felt a huge level of frustration that we could have been in Ikea or Tesco but we were on the beach taking part in the sport which we love and we had to deal with that afterwards.
"More or less everyone left the beach. I just find it incredibly sad that the public resources of the police are being used to close down beaches for no reason."
Mr Murphy said after he came out of the sea and was getting changed he was approached by six police officers.
He said he had seen them from the water walking "systematically, approaching groups and threatening them with £200 fines".
"I pointed out we could be at Ikea or Tesco. They said: 'This is an organised event'. We pointed out this is not, this is people taking part in something healthy."
'Big enough beach'
Cathy Martin, who lives in Helen's Bay, said she took a walk down to the beach with her children and dog. She told the Stephen Nolan Show it was busy, but that a lot of people there were residents.
She said she was then told by police officers that she would have to leave the beach as well.
"They basically came with the attitude that everyone was there for an organised event," she said.
"They're under a lot of pressure, they're under-resourced and they have a lot to cover, and I do respect that they have to respond to every complaint and I do respect that there probably was a complaint from residents about a lot of cars there or a lot of people there.
"But Helen's Bay is a big enough beach to hold 200 people, it doesn't justify them coming to break it up."
In a statement the PSNI said: "Our approach has been that we will engage, explain and encourage members of the community to comply with the Health Protection Regulations.
"The vast majority of our community are complying with the restrictions, which we all recognise, are asking people to restrict their personal and professional lives in a way none of us would ever have thought possible.
"While enforcement is our last resort, we have not, and will not, shy away from enforcement when it is necessary."