Australia's largest coal producer has been fined for causing serious environmental harm by dumping 3000 tonnes of silt and sediment into Queensland's Isaac River.

The BHP Mitsubishi Alliance (BMA) has been penalised $200,000 for the unauthorised and uncontrolled release of mine-affected water at its Goonyella site in June and July 2017.

A truck on-site at the Goonyella Riverside Mine. Credit:Peter Braig

The open-cut coalmine operator self-reported the release, which caused about 3000 tonnes of sediment and silt to end up in the river system.

In Emerald Magistrates Court this month, BMA admitted causing serious environmental harm after telling Queensland's Department of Environment and Science.