The only bottlenose dolphin pod in England, known to travel along the Devon coast, is at risk from human and environmental factors.
A pod of dolphins was recently spotted on the river Dart, swimming past boats near Dartmouth.
The warning comes from the University of Plymouth, Cornwall Wildlife Trust and the South Coast Bottlenose Consortium after a decade of research. They estimate the dolphin pod currently consists of just 48 individuals.
They now want urgent measures to protect the population and its habitats, or risk the possibility the pods extinction. Researchers said the pod's territory off the English Channel coast was known to suffer from repeated and prolonged spells of pollution and fishing pressure and the fact they inhabit some of the busiest shipping lanes in the world.
Associate Professor of Marine Conservation at the University of Plymouth, Dr Simon Ingram, leads the bottlenose dolphin research project, said: "This population lives along one of the most developed and busy coastlines in the world which poses a clear threat to their conservation,
"To see the south coast population decline to extinction would be a local tragedy for the dolphins and for us."
A citizen science network of boat owners, ecotour operators and members of the public, established to pool sightings, revealed that dolphins from this pod travel the coast between North Cornwall and East Sussex.
The team found the population appeared to be isolated with individuals known to socialise within their own pod close to the shore but not with others from other populations normally found in the open sea.
Researcher Shauna Corr added: "Conservation measures to protect these animals have previously been hindered by a lack of knowledge of population size, distribution, and ranging behaviour. Thanks to a citizen science network stretching right along the English Channel and beyond, we can now fill these knowledge gaps."