Contact Energy is investigating how a slip at its Wairakei Power Station site polluted the Waikato River today.
The company said muddy water flowed into a tributary that fed the river upstream of the Huka Falls.
Contact Energy head of geothermal operations John Clark said a pollution response team and environmental specialists were investigating.
"We are working with the local councils to assess the impact of this. We are conducting precautionary tests on the water and are working with stakeholders in the Wairakei area to ensure they are informed," he said.
Mr Clark said water supplies for most of Taupo were unaffected.
Waikato Regional Council warned people downstream of the falls to be careful using any river water, which had turned brown.
Regional and district council staff have collected water samples for testing and they are contacting water users.
Initial reports suggest a holding pond wall collapsed, the council said.
Taupō-based regional council staff have this afternoon collected water samples for testing, with incident response staff also now at the scene.
The Tūwharetoa Māori Trust Board has been advised of the incident, and Taupō District Council staff have also collected samples.
Taupō District Council has shut off its Centennial Drive water supply intake and is asking users of that scheme to conserve water.
The scheme supplies Centennial Drive and Rakaunui Road users, as well as the local golf club and the pool at the Top Ten Holiday Park.
The district council is working on providing an alternative treated water supply from the Taupō town scheme to continue to provide treated water to those who need it.