Rescuer on Monday saved seven dolphins that were among two dozen that became stranded in a river in southwest England, but the rest of the marine mammals died.
Rescuers believe a pod of about 15 dolphins swam up the Percuil River in Cornwall and were beached, and that other dolphins responded to their distress cries.
The Coastguard said the arrival of the first pod was reported Monday morning, and that most of that group had died.
Tony Woodley of British Divers Marine Life Rescue said this was the biggest mass stranding of marine life in Britain for 27 years and said most of the dolphins would probably die.
"We haven't seen a stranding anywhere near this scale since 1981, when pilot whales were beached on the east coast. This is extremely rare," he said.
Woodley said the striped dolphins normally did not swim near coasts, but perhaps they had moved in to feed on fish attracted to a large algae bloom.
"Logistically a rescue like this is a minefield. It is very difficult to manage," Woodley said. "You have to get all the dolphins together. If one or two leave the river system, they will just come back to rejoin the main social group."
The Royal National Lifeboat Institution said that its volunteers did guide some dolphins back into deep water.