Lake Waahi (or Lake Waihi) is located west of Huntly, linked to the Waikato River by way of a weir onto the short Waahi Stream. Lake Waahi is the third largest lake in the Waikato Region. The smaller Lake Puketirini is immediately southeast. The lake is supertrophic, meaning it is very nutrient enriched (www.waikatoregion.govt.nz). The primary causes of water quality decline have been mine discharge, increased agriculture, clearing of native forest and the resulting increase in nutrient and suspended sediment levels (www.lernz.co.nz).
The water quality of Lake Waahi has improved since the 1970s and 80s following the control of coal mining activities in the catchment and the return of submerged aquatic plants. Further improvement may occur if the abundance aquatic plants continues to increase (www.waikatoregion.govt.nz).