The creases still visible on its body, caused by the way baby whales develop folded in half in the uterus, showed it was a newborn. Project Jonah volunteers confirmed it was still suckling.
The stranded female found on Ninety Mile Beach was not lactating so was not its mother.
Meanwhile, five adult dolphins seen far inland up a Far North creek are thought to have returned to safety.
She said it was natural for dolphins to venture into estuaries and up rivers to feed, but in this case they may have misjudged the tide.
Residents became concerned when the dolphins were confined to a small area of river at low tide and could not return to the sea.
Ms McDowell said as long as dolphins were not cut off from the sea for long periods of time, stayed wet and were moving, they were okay.
"It's when they stop moving and stay close to river banks that we start to worry, as this is a sign of stress," she said.
The dolphins stayed up river for two high tides before finally returning to the Rangaunu Harbour.
She thanked residents who called DoC's Kaitaia office about the dolphins.
It was only with the eyes and ears of local communities that DoC was able to help native mammals in distress, she said.
Call 0800 DOC HOT (0800 362 468) with any concerns about the welfare of marine mammals or native wildlife.
