A "superpod" of around 1,500 dolphins has been captured on film off the coast of Pembrokeshire by conservationists.
Eight volunteer members of the Sea Trust came across the "mile-long wall of dolphins" near the Smalls Lighthouse in the Irish Sea.
The charity's founder Cliff Benson said in wildlife terms the sight "was like winning the lottery".
Meanwhile Sea Watch said there had been dolphin sightings off parts of the Welsh coast they rarely visit.
The Sea Trust volunteers had been carrying out a small boat survey around the Pembrokeshire islands.
Mr Benson said: "As we were approaching the Smalls Lighthouse the sea was quite choppy, the sky grey and overcast.
"Suddenly in the distance we saw what appeared to be a blizzard.
"As we approached, we realised that the "blizzard" was thousands of Gannets spread out over a mile or more.
"Beneath them was a living wall of dolphins - a mile long and several deep.
"They just kept on coming pod after pod passing by the boat. Some came and looked at us but most just kept on going.
"This must have been a combination of many smaller pods joined together to exploit a huge bait ball of fish. It was possible to see all ages of dolphins from big adults to tiny babies."
He said it was the second time the Pembrokeshire-based charity had witnessed such a phenomenon.
"Back in August 2005 we had another superpod which I filmed and which was then shown around the world," added Mr Benson.
"I did not expect to see such an awesome sight again in my lifetime, this was in wildlife terms like winning the lottery a second time."
In a separate development, the marine research and education charity Sea Watch has called for an extension to the Special Areas of Conservation for the species within Cardigan Bay.
It follows sightings in the past few weeks of bottlenose dolphins off Anglesey and Rhyl on the north Wales coast and Gower on the south.
Research director Peter Evans said: "Our surveys and photo ID research are revealing just how far the bottlenose dolphins from Cardigan Bay can range not just in winter but in summer too.
"These sightings have important implications for the wind farm developments at nearby North Hoyle and Gwynt y Mor since there has been cause for concern over possible disturbance during both the construction and production phases.
"Under the EU Habitats Directive, bottlenose dolphins require specific protective measures and that's why two of three SACs in the UK were created in Cardigan Bay for the species.
"However, we now know that the Cardigan Bay animals are regularly coming here as well, so that conservation management must extend to this region."