The mercury found in streams at Puhipuhi near Whangarei is no threat to human health, the Northland Regional Council says.
An anti-mining group said tests done by the council and local hapu showed high levels of mercury and it was worried an abandoned mercury mine was polluting local waterways.
However the council said the area was naturally rich in mercury.
Its Maori advisory chair, Dover Samuels, said the mercury levels in the streams still met the New Zealand drinking water standard, although they were higher than in other areas.
He said he supported the group's call for ongoing monitoring and the remediation of the old mine workings and quarry.
Mercury was mined intermittently at Puhipuhi in the first half of last century.
A number of local families said relatives who worked at the mine had no protective gear, and became ill from breathing the toxic vapours.
