Which Indonesian lake contains Samosir Island?

Lake Toba is the Indonesian lake that contains Samosir Island.

Located in North Sumatra, Lake Toba occupies the enormous caldera of the Toba supervolcano. Samosir is a large volcanic island formed by uplift within that caldera, making it a striking island inside a lake that itself occupies a volcanic crater. The island covers about 630 square kilometres and is a major centre of Toba Batak culture.

The landscape formed after a supereruption roughly 74,000 years ago, one of the largest known explosive eruptions of the Quaternary period. The collapsed caldera later filled with water, while renewed uplift produced the island and other elevated features in the lake.

Samosir is sometimes confused with the lake itself because both names are closely associated with tourism and Batak heritage. Lake Toba is the water body; Samosir is its prominent central island. The lake is about 100 kilometres long, up to 505 metres deep and drains through the Asahan River.