Kyle of Sutherland (Scottish Gaelic: An Caol Catach) is a river estuary that separates Sutherland from Ross-shire. It flows into the Dornoch Firth and is fed by the rivers Oykel, Shin, River Cassley and Carron.
The downstream extent of the Kyle of Sutherland is the bridge at Bonar Bridge. The upstream end of 'the Kyle' as it is locally known is the furthest inland extent of tidal water, which corresponds to 'the bailey bridge', beyond Rosehall.
The Kyle did separate Sutherland-shire and Ross-shire for centuries until 1975 when The Highland Region reorganised its internal boundaries leaving both banks within Sutherland.