Waikato Regional Council is investigating a significant unauthorised discharge of lime from the Golden Cross Joint Venture gold mine’s wastewater treatment plant into the Waitekauri Stream at Waikino.
The mine says the discharge followed an act of vandalism at the Golden Cross Rd plant on either Tuesday night or early Wednesday morning this week.
A quantity of lime from a tank got into the stream and is having effects on aquatic life up to three kilometres downstream of the discharge point.
“Lime can be toxic to aquatic life,” said council scientist Dr Bruno David.
“Our initial investigation has found koura, eels and aquatic insects have been affected and that there is evidence of residual lime remaining in the waterway.”
However, early indications are that the bulk of this residual lime is near the discharge point and that there is not a risk to animal and human health further downstream, the council said.
The investigation is looking into how the discharge happened and what quantities of lime have been discharged, and assessing the full impact on aquatic life and the health of the waterway.
The council is considering what could be done to remove residual lime. Further discussions on this will be held after the council sees what impact the weekend’s weather has on the stream and the lime remaining in it.