Even brief disturbance can cause adult birds to leave their nests, leaving eggs and chicks vulnerable.
Hartlepool Borough Council’s director of communities, Gemma Ptak, said the majority of dog owners were being considerate but it was “really disappointing” that some were taking their pets into the exclusion zone.
“This not only risks the beach not being clean for the visitors who use it, especially children, it also puts the fragile nesting of the little terns in jeopardy,” she said.
“We would urge people to report any breaches of the dog exclusion zone to us.”
Little terns, the smallest terns in the UK, typically leave Seaton Carew in mid-to-late August, having migrated from West Africa.
The species is currently classed as being in the “amber” category on the UK list of conservation concern.