Waikato Regional Council monitors water quality at 10 sites along the Waikato River, the largest, most intensively used river in the region.
It also monitors water quality at another 100 sites on other rivers around the region, including the Waipa, Mokau, Awakino Waihou, Piako and Tongariro.
Water quality is better in some parts of the region, for example the Coromandel Peninsula and the catchment of Lake Taupo, than in others such as the lowland Waikato basin and the Hauraki Plains. This is mainly because of the greater intensity of land use in the lowland parts of the region.
Water quality tends to be poorest in areas of intensive farming, including the extensive areas of dairy farming for which the region is known.
River water quality varies from excellent to poor, and in less developed parts of the region conditions are excellent and there have been few signs of deterioration. But water quality is poorer in intensively farmed areas and concentrations of nitrogen have steadily increased over the past two decades of monitoring.
During summer, some freshwater bathing sites are monitored on a weekly basis.