More than 20 people linked arms to enter the sea and successfully bring the swimmer in strife in rough sea back to shore.
The coastguard said the swimmer was unhurt but warned against going in the sea in windy conditions.
A witness stated:
“I was certain it would end differently. It was unbelievable – what selfless, selfless people.”
A statement by Lulworth Coastguard Rescue team said: “With the large waves and spring tides of late, we strongly discourage sea swimming and playing around in the surf, especially on exposed beaches such as Durdle Door.
“The undertow is very powerful and will have no trouble taking you off your feet.”