The Department of Environment and Heritage Protection is investigating after reports several tonnes of caustic soda spilled into Gladstone Harbour.
The department said the spill could affect the local marine ecology and damage boats that come into contact with the chemical.
In a statement, the EHP said it was notified an unconfirmed amount of sodium hydroxide had leaked into the harbour from a vessel berthed at Queensland Alumina Limited wharf about 12am on Monday.
Officers from the department assessed the site first thing on Monday morning and were continuing to investigate exactly how much of the chemical had spilled into the water.
Queensland Parks and Wildlife Service staff were been using a boat to visually check the shoreline for any signs of damage.
QAL has been contacted for comment.
