|Mouth||Carnikava, Gulf of Riga|
|Basin countries||Latvia, Estonia|
|Length||452 kilometres (281 mi)|
|Basin area||8,900 km2 (3,400 sq mi)|
The Gauja River is a river in Vidzeme, Latvia. It is the only river out of the large rivers of Latvia, which begins and ends its flow in Latvia. Its length is 460 km, of which 1/5 or 93.5 km are in Gauja NP. In this part, the Gauja River flows through a spacious ancient valley, which is 1 to 2.5 km wide, and the maximum depth near Sigulda is 85 m. The Gauja River is known for its beauty.
The beautiful sandstone rocks on the banks of the Gauja and Its adjoining rivers started formation before 370–300 million years during the Devonian era.
The valley of the Gauja River started formation approximately one million years ago in the Quaternary geological period. The final formation of the ancient valley of the Gauja River occurred during the glacier activity period. The glaciers melted and covered the territory of the Gauja National Park anew for several times, the flows of melting waters settled in the terraces of the Gauja and brought fieldstones, gravel, and clay. The ancient valley of the Gauja River gained its current look gradually during the last 10 000–20 000 years.
The Gauja River used to serve as a trade route and border river between the Livs (Finno-Ugrian) and Latgalians (Indo-European) lands. In some territories, they used to live mixed together. The Livs suffered greatly during the Northern War and plague in the 18th century. That was the period when the remaining Livs assimilated with Latvians. When Liv’s languages were still present along the Gauja River and the sea, it used to be called Koivo – Bērzupe or Svētupe (the Saint River) (derived from the Finno-Ugric languages). In Latvian the name of the Gauja River used to mean ‘a great amount’, ‘a crowd’, and therefore, was called the ‘big river’.
The Gauja River tends to change its bottom rapidly. Therefore, it has gained the reputation of being deceitful. The bottom of the river is made of unconsolidated sand and gravel deposits, which move along with the torrent. In some places, the bottom is pebbly, thus forming impressive boulder rapids – Kazu, Raiskuma, Rakšu, and Ķūķu. The bottom of the river in the part of the Gauja National Park is 60 to 120 meters wide with rapidly changing depth from 0.3 m to 7 m. The torrent decline is 0.5 m/km. The speed of the flow during the low water period is 0.2-0.4 m/s, and during the spring water period 2–3 m/s. Due to the fluctuations of water level, torrent speed, and peculiarities of the flow, the Gauja River could be characterized as rather non-homogeneous watercourse.
Usually the Gauja River freezes over in the mid-December, and the ice starts moving during the third decade of March. During warm winters, the river does not freeze over. Plenty of underground water flows into the River Gauja. Therefore, it has lower water temperature than in the rest of the bigger rivers of Latvia.