The 9.7m long juvenile humpback was first seen floating off the coast of Warrington two weeks ago and was found washed up last week at Omimi.
Department of Conservation biodiversity ranger Jim Fyfe said the whale posed health risks to people.
Whales were mammals that carried bacteria and diseases which could be passed on to people.
Swimmers and surfers in the area needed to be aware the whale could spark an increase of sharks in the wider area, such as Warrington Beach.
He also asked people to stay away to respect the privacy of neighbouring landowners.
The most direct access to the beach crossed private property and the landowners were not able to accommodate people wanting access to see the whale.
The site was difficult to access by land and water and it was not practical to remove or bury the carcass.
It had been thought the whale might wash back out to sea with the heavy swells this week, but now it was likely to stay beached for several months while it decomposed.
Throughout that time the whale would start to smell and the common northeast wind would probably push that along the coast.
It was possible it could attract rats as well, as they were a known pest on the coast, but Doc would work with the neighbouring residents to keep track of the situation.
It would also work with Kati Huirapa Runaka ki Puketeraki to monitor the decomposition of the whale.
Staff would also be meeting the Warrington Surf Life Saving Club to discuss risk assessment when planning events in the lead-up to summer.
Club chairwoman Charlotte Becconsall-Ryan said sharks were a common occurrence, but the possibility of an increased population meant the club would need to focus on prevention.
She did not anticipate any events would be cancelled because of the sharks.
Although it did create some problems, the beached whale provided an opportunity to watch nature take its course, she said.
Mr Fyfe said a DNA sample had been taken from the whale and the cause of death was still unknown.
Humpback whales could be seen off the Otago coast as they migrated north away from the cold Antarctic waters between May and July, but it was unusual for them to wash up, he said.
