Okuru woman Nicole Buchanan spotted them last week, and a friend saw them two weeks before that, off the Okuru River bridge.
"I was in the back of a vehicle and thought, that’s a big fish."
She had heard of other sightings in the past, but not that far inland — 4km or 5km.
Ms Buchanan heard one making a call. No stranger to Hector’s dolphins, she sometimes swims with them at Neils Beach.
Kerry Eggeling, also of Okuru, said for nearly a month three dolphins had been frolicking in the river and the shared lagoon of the Okuru, Turnbull and Hapuka Rivers.
Department of Conservation marine reserves ranger Don Neale said they also had a report of orca (killer whales) chasing Hector’s dolphins at Ship Creek two weeks ago and, about the same time, a Hector’s dolphin and its calf were seen several times in the Hapuka estuary area.
"So it’s hard to be sure, but it sounds plausible that a few dolphins have recently been using the Haast rivers and lagoons to get away from predatory orca."
Hector’s dolphins have also been recorded in Ōkārito Lagoon on occasions.
While up the rivers, the dolphins may well feed on fish there.
"But it’s not common for them to swim up rivers so I suspect that the food isn’t their main reason for being there."
Mr Neale said it could sometimes be hard to see dolphins in murky water because they surfaced only every few minutes to breathe.
"We have generally found that locals do take care to let each other know about dolphins in estuaries and to ensure their protection and the dolphins have typically stayed in the rivers for no more than a few days."
