Lifeboat crews have been called out five times to rescue walkers from a Welsh island since lockdown began.
People get trapped on Sully Island - between Penarth and Barry in the Vale of Glamorgan - as it is accessible at low tide and then get stuck once the water starts to rise.
The RNLI said ramblers were making more effort to get there as the mainland car park was shut.
Crews said they were put at risk of catching coronavirus on each call-out.
RNLI Barry Dock's Nigel Parry said: "It is putting the crew members in danger because they have got to assemble in the station, bearing in mind social distancing.
"When they launch they are in a D-class lifeboat where they cannot be two metres apart.
"They are then in contact with the people on the island."
The latest rescue was at about 17:00 GMT on Wednesday when a man had to be brought back to shore - almost exactly a month since lockdown started.
"There seems to be increased amounts since the lockdown, which is bizarre," Mr Parry said.
"The car parks are blocked off so people making are making a deliberate attempt to get there."
He said there had "historically" been a problem with people getting stuck on island.
"The danger is that people who get stranded attempt to walk back," Mr Parry said.
Mr Parry asked people to think "long and hard" about whether they needed to visit the island.
"They could be putting people's lives at risk," he added.