The Whangamarino River is a lowland river of the Waikato Region of New Zealand's North Island, draining the Whangamarino Wetland and associated farmland catchment. The river converges with the Waikato River just north of Meremere. The main tributary is the Maramarua River, which starts in the Hunua Ranges and forms the northern catchment of the Whangamarino River.
The natural Whangamarino River system, especially the main branch (the southern catchment), has been highly modified due to the lower flood protection scheme of the lower Waikato River. Prior to these floodworks, the Whangamarino Catchmet was unconnected with Lake Waikere. However due to the Lower Waikato-Waipa Flood Control Scheme, constructed in the 1960s, Lake Waikere was transformed and used for flood retention storage when the nearby Waikato River was in flood. During flood events, the Waikato River now overflows into the transformed Lake Waikere via the Rangiriri Spillway (and the redirected Te Onetea Stream). When the Waikato River conditions are suitable, the flood waters are discharged from Lake Waikere into the Whangamarino River catchment through the artificial Pungarehu Canal.
While the flood scheme has permanently changed the ecology of Lake Waikere, it has also provided broader benefits for the community.
The Whangamarino River includes the large Whangamarino Wetland (5,193 hectares) which is the second largest bog and swamp wetland in the North Island of New Zealand (after the Kopuatai Peat Dome). Due to human activity of draining the wetland for farming and the impact of the flood control scheme, the size of the wetland is about half its natural size. The wetland includes peat bog, swampland, mesotrophic lags, and open water river systems are managed as both Wetland and Wildlife Management reserves by the Department of Conservation. Importantly, the Wetland is protected by under the Ramsar Convention (Wetland Protection Treaty).