There is some place off the Florida coast which has a fresh water spring in the ocean. In olden times ships would stop there and refresh their water supplies.
I dove on a fresh water upwelling in the Gulf of Mexico. When the dive master told us what it was, I took my regulator out and swallowed some of it. It was clean and pure.
When I was a kid there was an old guy that went to sea with his dad when he was 8 years old. He said they took on fresh water off the Amazon river 100 miles out while sailing past.
Flying saucer pilots use them to drink fresh water. Worked long before the bottled water they use during patrols today.
Source is an underground civilization with space aliens who pilot submersible vehicles that break through to the air and soar at Mach 10. USO= Unidentified Submersible Objects.
None of the above is true but I find the speculative (nonsensical) books fun to read. Atlantis Rising Magazine just went out of business in May but Fate Magazine is still around since my childhood. Fun stuff. Gets my mind off politics for a while.
Same think still in the Persian Gulf. They get fresh water from springs on the floor of the Gulf.
Blackbeard Is. on the coast of Georgia has the same reputation. Ships could pass over and get fresh water for drinking out of the sea.
I think it was part of Grey’s Reef, but, due to the pumping of fresh water on land, the water table is too low for it to come out any more.