The River Spey is one of the largest rivers in Scotland, having a total catchment of 3008km2. The river network extends to some 36400km2 of which the main stem comprises 157km. From its source, Loch Spey (350m above sea level in the Monadhliath Mountains), the river travels in a northeasterly direction to discharge into the Moray Firth at Tugnet. In comparison with other UK rivers the Spey is ranked eighth in terms of mean annual flow, seventh in terms of its length and ninth in terms of catchment area.
A feature unique to the Spey is its rejuvenated character. The upper catchment is relatively steep as is the lower river downstream from Grantown. However, the middle part is characterised by a broad meandering channel, wide flood plain and is relatively slow flowing due to the low gradient. This area, known as the Insh Marshes, is more similar to a lowland river in form.
The Meterological Office currently monitors rainfall throughout the catchment at 26 sites. Mean monthly rainfall indicates that rainfall is generally highest in the upper catchment and lowest on the Moray coast. In general most of rainfall occurs from August through to February and is driven by frontal systems. Much of the precipitation during winter can lie as snow, which in the higher altitudes can become semi-permanent snow packs. These play an important role in maintaining flow levels well into summer and give the Spey an essentially alpine flow regime.
Water quantity and river flow is extensively monitored by the Scottish Environment Protection Agency (SEPA) using an array of gauging stations throughout the river. The range of flows experienced by the Spey is considerable, from 9.6 cubic metres per second to 1675 cubic meters per second (recorded during a major spate in August 1970). The lowest flows are generally recorded in summer although severe frosts can also considerably reduce winter flows. There is no general season for floods.
Water coming in from Loch Spey heading to loch laggan
In common with many Highland rivers, the waters are low in nutrients and, with a lack of major industrial developments within the catchment, the Spey has remained fairly free of pollution. Indeed the catchment of the Spey is considered to be almost 'pristine'.
The Spey is similar to many Scottish Highland rivers and supports only a limited number of fish species. These include: Atlantic salmon; trout as migratory sea trout and resident brown trout; European eel; Arctic char; pike; minnow three-spined stickleback and flounder. In recent years a number of local lochs have been stocked with rainbow trout, which have subsequently found routes into the Spey itself. However, there is no evidence that they have established a breeding population.