A Mangere East company has been fined $81,000 for discharging sediment and diesel into a stream which flows into the Manukau Harbour.

Specialised Container Services has two previous convictions for discharging dust and sediment from its container park in Savill Drive.

It's now copped a third conviction for discharges into Harania Stream in December and January.

The stream is a significant breeding ground for threatened species, including whitebait, banded kokopu and inanga.