Altnabreac (/ˌæltnəˈbrɛk/ ALT-nə-BREK, from Scottish Gaelic Allt nam Breac) is a tiny settlement within the county of Caithness, in the north of Scotland, and now within the Highland council area. The name means "trout stream".

It is located on Altnabreac Moss by the Sleach Water in the Flow Country, 9 miles (14 kilometres) east of Forsinard and 23 mi (37 km) west of Wick. The settlement, notable for its remoteness, consists of Altnabreac railway station and the former Altnabreac School. The school was closed in 1986 and converted into a private residence. The former gamekeeper's house sits adjacent to the school and station. There is a natural spring about 200 metres (650 ft) from the school.

Lochdhu Lodge, approximately 1+1⁄2 miles (2.5 kilometres) south, was built in 1895. During the 1980s peat banks were worked to provide fuel for the residents who regularly used to be cut off from the nearest town of Thurso during the winter. It can only be approached by train by special request to stop at the unmanned station, or along unsurfaced Forestry Commission roads from the nearest village, Westerdale, about 12 mi (19 km) away.

Altnabreac, like Dounreay, was considered as a location for a final repository for the UK's nuclear waste. This idea was not pursued.

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