Rotten Island lighthouse, lighthouse in Ireland

Rotten Island Lighthouse is a conical tower of cut granite, painted white, standing on a small island in Donegal Bay. It guides vessels from St. John's Point through the inner channel past the rocks to the anchorage in Killybegs Harbour. The tower and the keepers' houses were designed by George Halpin, and the station is operated by the Commissioners of Irish Lights.

A light was proposed for Drumanoo Point in 1832, but George Halpin recommended Rotten Island, and Trinity House sanctioned it in 1833. Halpin designed the granite tower and keepers' houses; the fixed white light was first shown on 1 September 1838, before the works were finished. Three men drowned on 15 September 1836 when their boat capsized while returning from the rock. The station was automated on 7 January 1959.

The Irish name is Teach Solais An tOileán Bréan, and the light marks the passage from St. John's Point into the inner channel and the anchorage at Killybegs Harbour. Mariners using the harbour complained when the 1959 automatic lens seemed weaker than the old light, and the station was converted to electric power on 1 February 1963.

The station can only be reached by boat; there is no causeway or low-tide path from the shore. The light marks the passage from St. John's Point into the inner channel and the anchorage of Killybegs Harbour, so approach by sea with local knowledge of the rocks. The light shows one flash every four seconds, a character set on 1 February 1965.

The station was automated on 7 January 1959, when the dioptric lens, its revolving machine and the vaporised paraffin incandescent burner were replaced by a fourth order cylindric refractor lens. Its acetylene mantle gave 2,600 candlepower white and 500 in the red sector, and mariners using the harbour complained it was worse than the old light.