Lake Taupō (also spelled Taupo; Māori: Taupō-nui-a-Tia or Taupōmoana) is a large crater lake in New Zealand's North Island, located in the caldera of Taupō Volcano. The lake is the namesake of the town of Taupō, which sits on a bay in the lake's northeastern shore. With a surface area of 616 km² (238 sq mi), it is the largest lake by surface area in New Zealand, and the second largest freshwater lake by surface area in geopolitical Oceania after Lake Murray in Papua New Guinea. Motutaiko Island lies in the southeastern area of the lake.

Lake Taupō has a perimeter of approximately 193 km (120 mi) and a maximum depth of 186 m (610 ft). It is drained by the Waikato River (New Zealand's longest river), and its main tributaries are the Waitahanui River, the Tongariro River, and the Tauranga Taupō River. It is a noted trout fishery with stocks of introduced brown and rainbow trout.

The level of the lake is controlled by Mercury Energy, the owner of the eight hydroelectric dams on the Waikato River downstream of Lake Taupō, using gates built in 1940–41. The gates are used to reduce flooding, conserve water and ensure a minimum flow of 50 m³/s (1,800 cu ft/s) in the Waikato River. The resource consent allows the level of the lake to be varied between 355.85 and 357.25 metres (1,167.5 and 1,172.1 ft) above sea level.

Lake Taupō is in a caldera created mainly by a supervolcanic eruption which occurred approximately 25,600 years ago. According to geological records, the volcano has erupted 29 times in the last 30,000 years. It has ejected mostly rhyolitic lava, although Mount Tauhara formed from dacitic lava.

Taupō has been active for 300,000 years with a very large event known as the Oruanui eruption occurring approximately 25,600 years ago. It was the world's largest known eruption over the past 70,000 years, ejecting 1170 cubic kilometres of material and causing several hundred square kilometres of surrounding land to collapse and form the caldera. The caldera later filled with water to form Lake Taupō, eventually overflowing to cause a huge outburst flood.

Several later eruptions occurred over the millennia before the most recent major eruption, which was traditionally dated as about 181 CE from Greenland ice-core records. Tree ring data from two studies suggests a later date of 232 CE ± 5 and this is now accepted. Known as the Hatepe eruption, it is believed to have ejected 100 cubic kilometres of material, of which 30 cubic kilometres was ejected in a few minutes. This was one of the most powerful eruptions in the last 5000 years (alongside the Minoan eruption in the 2nd millennium BCE, the Tianchi eruption of Baekdu around 1000 CE and the 1815 eruption of Tambora), with a Volcanic Explosivity Index rating of 7; and there appears to be a correlation, to within a few years, of a year in which the sky was red over Rome and China. The eruption devastated much of the North Island and further expanded the lake. The area was uninhabited by humans at the time of the eruption, as New Zealand was not settled by Māori until about 1280. Possible climatic effects of the eruption would have been concentrated on the Southern Hemisphere due to the southerly position of Lake Taupō. Taupō's last known eruption occurred around 30 years later, with lava dome extrusion forming the Horomatangi Reefs, but that eruption was much smaller than the Hatepe eruption.

Underwater hydrothermal activity continues near the Horomatangi vent, and nearby geothermal fields with associated hot springs are found north and south of the lake, for example at Rotokawa and Tūrangi. These springs are the site of occurrence of certain extremophile micro-organisms, that are capable of surviving in extremely hot environments.

The volcano is considered active and is monitored by GNS Science.