The Waikato is New Zealand’s longest river, central to the identity and practices of Waikato River iwi and a source of drinking water for nearly half of the country’s population.

It is also becoming a case study in what happens when very different environmental pressures hit the same system faster than authorities can respond.

A recent RNZ investigation documented worsening toxic algal blooms in hydro lakes in the upper Waikato. Communities around Lake Ohakuri describe water so green it resembles the “Incredible Hulk”, dogs becoming violently ill and mats of toxic slime covering the surface.

These conditions are a long way from Te Ture Whaimana o te Awa o Waikato, the legislated vision for a river safe for swimming and gathering food.

The reporting captured genuine community frustration and institutional fragmentation. But to turn concern into effective action, we need to understand why blooms keep forming where they do.

Otherwise, interventions risk missing the mark. The Waikato cannot afford misdirected effort.

The location of the worst blooms is a clue. Lake Ohakuri sits right next to the Ohaaki-Broadlands geothermal field, where decades of extracting hot fluids for power generation have caused the ground to sink by nearly seven metres.

That geothermal activity releases heat, carbon dioxide (CO₂) and mineral-rich fluids into the........

© The Conversation