Moray Firth the Moray Firth and Highland, Moray and Aberdeenshire to the south. The firth has more than 800 kilometres (about 500 miles) of coastline, much of which is cliff. A number of rivers flow into the Moray Firth, including the River Ness, the River Findhorn and the River Spey. Various smaller firths and bays are inlets of the firth, including the Cromarty Firth and the Dornoch Firth. The Pentland Firth has its eastern mouth at the Moray Firth's northern boundary. The Moray Firth is effectively two firths, the Inner Moray Firth , which was traditionally known as the Firth of Inverness,
Firth "firth" (e.g. the Minch and Loch Torridon); instead, these are often called sea lochs. Before about 1850, the spelling "Frith" was more common. A firth is generally the result of ice age glaciation and is very often associated with a large river, where erosion caused by the tidal effects of incoming sea water passing upriver has widened the riverbed into an estuary. Demarcation can be rather vague. The Firth of Clyde is sometimes thought to include the estuary as far upriver as Dumbarton, but the Ordnance Survey map shows the change from river to firth occurring off Port Glasgow, while