Lake Rotorua is the region’s oldest lake. It is thought to have formed shortly after the Mamaku Ignimbrite eruption about 140,000 years ago, and it occupies a caldera created by the event. Lake Rotorua has the largest surface area of the district’s lakes. It also has the largest catchment area at about 508 sq km. Pasture is the main land cover in the catchment, followed by indigenous vegetation (source www.lawa.co.nz).