Holtsós, sometimes anglicised as Holtsos, is a tidal lagoon south of Eyjafjallajökull in south Iceland. It is fed by the Holtsá river and separated from the Atlantic Ocean by a narrow strip of sand.
It is approximately 4 kilometres (2.5 mi) long by 2 kilometres (1.2 mi) wide and approximately 2 metres (6.6 ft) deep at its deepest point.