Metropolitan Police officers were called to Ruislip Lido in west London to reports of a large group gathering there.
The Government has urged people to continue to follow social distancing guidelines.
“Please use common sense when it comes to social distancing,” the Met’s Hillingdon branch tweeted.
Elsewhere, crowds flocked to beaches and parks to enjoy more good weather, a week after the Government relaxed guidance to allow people to visit beauty spots in England.
Walkers were seen enjoying the grounds of Windsor Castle.