The Auckland Council says it is too early to tell whether a large spill of purple dye into some waterways will have a long-term effect.
The dye was first noticed around the Manukau Harbour near Montgomerie Drive and Ruaiti Road. It has come from a company based near the airport that colours food packaging.
A council spokesperson said on Tuesday the dye has killed some eels and other fish and coloured the banks and stream bed.
The council tried to contain and clean the spill but now hoped that tides would bring the water quality back to normal.