The Grade II listed Clifton Lido, which has been shut for 18 years, reopened on Monday following a £2m facelift.
Jonathon Bradshaw, who is planning to swim across the Atlantic from Cape Cod to Ireland, was the first in the pool.
BBC Radio Bristol's Ben Prater also got the chance to have a swim in the pool which is heated by solar power.
The revamped lido also includes a new spa and restaurant which overlooks the pool.
The lido, designed by Bristol architect Richard Shackleton-Pope in 1850, has seen many campaigns to preserve it.
It closed in 1990 and in the following 18 years a campaign was fought to stop it being demolished.
Planning permission to restore the site to its former glory was granted to new owners, the Glass Boat Company, in 2007.