Strepto

Strepto was the home planet of the Water Hags. Its landscape was mainly comprised of a marsh-like, boggy terrain. It was apparently lost by the Water Hags, who claimed it vanished into thin air. (TWN: Something in the Water)

In fact, the planet had been stolen by the Daleks and was one of the 27 planets they needed to activate the reality bomb. It was returned to its rightful place and time. (REF: The Time Traveller's Almanac)