It comes after more than 40 dead little blue penguins were found washed up on Tokerau Bay, just around the corner from Cable Bay in May.
An investigation by the Ministry for Primary Industries showed the kororā had signs of starvation and hypothermia, due to a lack of blubber to keep them warm in the water.
The penguins had poor body condition and their gastrointestinal tract was empty, DoC said.
Later in May, more than 100 little blue penguins were found dead on Ninety Mile Beach (Te One-roa-a-Tōhē), according to photographs on social media.
Kororā were once common on the mainland coast. Now, most are found on offshore islands where there is less disturbance from humans, dogs, and introduced predators, DoC said.
Despite this, kororā can be found on beaches around the country, and their population is increasing in areas where there is predator control.
Every year starting around November, DoC begins to receive reports of dead kororā washing up on beaches, and bird rescue centres get an influx of sick and injured birds to care for.
The summer of 2020/21 is a La Niña year. This brings increased sea-surface temperatures and onshore winds to New Zealand. These conditions can make it more challenging for kororā to nest and feed.
However, DoC said some level of mortality is natural and to be expected.
DoC advises people can help the penguins by keeping their dogs on a leash in coastal areas and away from nests.
It advises anyone who finds a dead or injured penguin to leave it where it is. Sick penguins at risk of attack from dogs can be placed under vegetation in rear dunes or taken to a local bird rescue centre.
DoC was asked about the Cable Bay dumping, but was unable to respond by publication time.
