Less than a week old and still fully furred, the male grey seal pup was spotted lying on rocks by men working on the new Forth Road crossing.
As the men approached the pup he fell off the rocks and into the water.
Grey seal pups cannot swim well until they have lost all their fur so the workmen fished the pup out of the water and called the Scottish SPCA.
Animal rescue officer Joanna McDaid took the seal to the charity's national wildlife rescue centre at Fishcross, Alloa, where he is now receiving treatment and care. Staff have named him Tiller.
Centre manager Colin Seddon said: "Tiller is our first grey seal pup of the season and he's quite unusual in that he was found in an area that is not a known pupping ground.
"He could have been washed off the established pupping ground at nearby Inchkeith Island or his mother may have been young and inexperienced.
"It sounds as though he took fright when he was approached and slid off the rocks and into the water which is bad news for a newborn seal pup as their thick fur coats act like a sponge and absorb water so he's unlikely to have survived on his own for long.
"Thankfully, the men scooped him out of the sea and called us for help."
He added: "He's being tube-fed fish soup at the moment and that will continue for the next few weeks until he's old enough and strong enough to feed himself."
The Scottish SPCA is now urging members of the public to contact its animal helpline if they see a distressed seal pup lying on the shore this winter, adding that they could be doing more harm than good by approaching or picking it up.
A newborn seal pup has been rescued by workmen after he fell into the sea at North Queensferry in Fife.