South Auckland residents are being urged to keep an eye out for flashes of purple feathers flying overhead.
Hundreds of litres of violet dye has spilled into a stream in Mangere, flowing into the Manukau Harbour.
New Zealand Bird Rescue says it will affect all the creatures which use the water, such as crabs and worms.
Spokesperson Hilary Stollery says the worst issue will be birds diving into the water and turning purple, which will destroy their feathers.
"We're going to have to keep it until all the feathers have moulted out and moulted in its new feathers.
"Also, I was told that it is an irritant."
Anyone who finds a coloured bird is asked to take the bird into care and contact Bird Rescue.