The Thames Valley is a non-administrative region in the North Island of New Zealand. Broadly, it is the valley component of the Waihou River catchment. The lower part of the valley is more commonly known as the Hauraki Plains. Geographically the valley extends as far as the Hinuera Gap, although this is not often referred to as such. In geographical history of New Zealand, the Thames Valley was the path of the ancestral Waikato River when it discharged into the Firth of Thames over 20,000 years ago.