Divers have mounted a special operation to relocate nearly 40 endangered seahorses discovered in tidal pools on Sydney's Northern Beaches.

Many of the rare White's seahorses found in pools at Clontarf and Balgowlah were pregnant, and had to be handled with extreme care.

White's seahorses are only found in Australia, and are only one of two endangered species of seahorse worldwide.

They were found by council workers preparing to conduct repair work on the Clontarf Beach and Forty Baskets tidal pools.

"We had no idea of their existence and then to be told we have a colony of these rare seahorses, we're pretty excited to play a part in protecting them," Mayor Michael Reegan said.

Care is taken to keep the lifelong couples together when they are moved. ( Supplied: Sea Dragon Protective Enclosures )

Divers also found eight pipefish, which look like straightened-out seahorses.

They are now safely moving all the seahorses to nearby seagrass beds.

The diver leading the relocation project, Carl Fallon from Sea Dragon Protective Enclosures, described the seahorses as "cryptic" and hard to find.

"It's like gold panning, you know when you find that nugget it's like 'boom, there you go you've got one', and once you start finding one you know that there's going to be more in the area," he said.

The extraordinary find has come at an important time of year for the seahorses — breeding season.

The seahorses are being moved to nearby seagrass beds. ( Supplied: Sea Dragon Protective Enclosures )

"The male animal gives birth, which is unusual in the animal kingdom, but they also fall in love — the seahorses pair up for life," said David Harasti, a senior research scientist with NSW Fisheries.

"It's a lovely relationship they have together in the underwater world."

Mr Fallon said his divers were careful not to separate the loved-up seahorses during the move.

"We're lucky enough to see pregnant males … so if we do see any that are close to each other during the relocation we put them in a bag [together]," he said.

White's seahorse population numbers have decreased dramatically in the past few years due to destruction of their habitat; primarily sea grass and sea sponges.

Carl Fallon (L) said divers are taking care to spot pregnant seahorses. ( ABC News: Cameron Gooley )

"In some places we've had declines of up to 90 per cent, so where we used to see around 400 seahorses we're down to about 10 animals now," Dr Harasti said.

According to Dr Harasti, man-made structures — like the netting at Clontarf Beach's tidal pool — are providing an alternative habitat for the endangered animals.

"These artificial structures are basically seahorse magnets, if you build it they will come," he said.

These seahorses might be endangered, but Mr Reegan thinks his newfound Northern Beaches residents are in safe hands.

"With the community around here, they love their natural environment so no doubt there'll be countless volunteers, as there are in places like Manly with the little penguins, to help look after the sea horses," said Mr Reegan.