The River Spey is a river in Scotland that runs 107 miles (172 km) to the Moray Firth at Spey Bay, making it the second longest river in Scotland. The Spey is unusual in that it increases speed as it flows closer to the coast, due to the surrounding geography. The mean flow is around 16 m/s making it the fastest flowing river in Scotland, possibly the UK (depending on what constitutes a river.) The Spey does not meander, although it does rapidly move its banks. South of Fochabers the banks are reinforced with a high earth barrier, but this has been broken by the river 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. The Spey railway bridge (now pedestrianised) Spey Bay to Garmouth was originally designed with the main span over the main flow of the river, however before construction was completed the river had changed its course and was running at one end of the bridge. The Spey changes its course very frequently, either (relatively) gradually as a result of deposition and erosion from normal flow, or in a matter of hours as a result of going into spate. The Spey spates very quickly due to its wide catchment area in the mountains, as a result of rainfall or snowmelt. Area of roughly two miles on either side of the Spey in the lower reaches are designated SSI (Site of Special Scientific Interest) as well as the extensive shingle systems at the Spey mouth.

Rising at over 1000 feet at Loch Spey in Corrieyairack Forest in The Scottish Highlands, 10 miles south of Fort Augustus, it descends to flow through Newtonmore and Kingussie crossing Loch Insh before reaching Aviemore at the start of Strath Spey ('Spey Valley'). From there it flows the remaining 60 miles north-east to the Moray Firth watering the many famous distilleries of Speyside, that produce more whisky than any other region. The Spey is one of very few rivers in the world that flow South-North. The river is also known for the quality of its salmon and trout.

The river traditionally supported many local industries, from the still popular salmon fishing industry to the shipbuilding industry. At one stage, Garmouth was the shipbuilding capital of the UK, with timber from the forests around Aviemore and Aberlour being rafted down to create wooden hulled ships.