[3] One proposal is a derivation from a Pictish cognate of Old Gaelic sceïd, "vomit" (c.f Welsh chwydu),[3] which is dubious both on phonological and semantic grounds.

It rises at over 1,000 feet (300 m) at Loch Spey in Corrieyairack Forest in the Scottish Highlands, 10 miles (16 km) south of Fort Augustus.

Some miles downstream from its source it is impounded by Spey Dam before continuing a descent through Newtonmore and Kingussie, crossing Loch Insh before reaching Aviemore, giving its name to Strathspey.

The Spey spates quickly due to its wide mountainous catchment area as a result of rainfall or snow-melt.

After leaving Loch Spey the river gathers numerous burns in the Corrieyarack, Sherramore and Glenshirra Forests.

At one stage, Garmouth functioned as the shipbuilding capital of Britain,[citation needed] with timber from the forests around Aviemore and Aberlour being rafted down to create wooden-hulled ships.

The River Spey is unusual in that its speed increases as it flows closer to the sea, due to a broadly convex long-profile.

South of Fochabers a high earth barrier reinforces the banks, but the river has broken through on several occasions, removing a large portion of Garmouth Golf Course, sections of wall surrounding Gordon Castle, parts of the Speyside Way and some of the B9104 road.