A female leopard seal, believed to be about 3 years old, has made herself at home at Friendly Bay since early Saturday morning.
While the seal was not at the beach yesterday afternoon, she had returned regularly for the past five days.
The Department of Conservation (Doc) has set up a cordon around the beach to try to keep people away from the mammal.
Despite this effort, leopard seal researcher Giverny Forbes watched a young boy throw rocks at the seal on Monday evening, and heard others also witnessed people getting too close and harassing the seal.
The seal had a small injury to the left side of her head and was not using her left eye, Miss Forbes said.
"I’m hopeful she will recover from it as it has started healing."
It was disappointing people did not always respect seals, as when they came to shore it was often to rest.
"The beach is their bedroom.
"It’s really important they are not disturbed in any way so they can get the rest they need after spending long periods at sea.
Doc Oamaru ranger Tom Waterhouse agreed with Miss Forbes and said leopard seals should not be disturbed.
"Leopard seals are impressive animals and having them visit our shores is a privilege," Mr Waterhouse said.
Leopard seals were not uncommon on Otago beaches at this time of the year, and the Oamaru Harbour was a "relatively common place" for them to appear.
While leopard seals were not generally aggressive towards people, they would defend themselves if they felt threatened.
"While they can look harmless, leopard seals can swivel around very quickly from their resting position to attack and can inflict serious injuries to dogs or people.
"They also can carry infectious diseases."
People should keep at least a 20m distance, refrain from making loud noises or throwing objects at them, keep other animals and children away and never feed or attempt to touch them.
Leopard seal sightings could be reported to Doc or Leopardseals.org for monitoring.
