Daugava

The Daugava (Daugova; Dźwina; Düna) or Western Dvina (Западная Двина; Заходняя Дзвіна; Väina; Väinäjoki) is a large river rising in the Valdai Hills of Russia that flows through Belarus and Latvia into the Gulf of Riga of the Baltic Sea. The Daugava rises close to the source of the Volga. It is 1020 km in length, of which 352 km are in Latvia and 325 km in Russia. It is a westward-flowing river, tracing out a great south-bending curve as it passes through northern Belarus.

Latvia's capital, Riga, bridges the river's estuary four times. Built on both riverbanks, the city centre is 15 km from the river's mouth and is a significant port.

Etymology
According to Max Vasmer's Etymological Dictionary, the toponym Dvina cannot stem from a Uralic language; instead, it possibly comes from an Indo-European word which used to mean river or stream. The name Dvina resembles strongly Danuvius which itself derived from the Proto-Indo-European *dānu, meaning "large river".

The Finno-Ugric names Vēna (Livonian), Väinajogi (Estonian), and Väinäjoki (Finnish) all stem from Proto-Finnic *väin, meaning "a large, peacefully rolling river".

Geography
The total catchment area of the river is 87900 km2, of which 33150 km2 are in Belarus.

Tributaries
The following rivers are tributaries to the river Daugava (from source to mouth):


 * Left: Mezha, Kasplya, Dysna, Laucesa, Berezauka, Eglona, Pikstere, Ņega
 * Right: Usvyacha, Palata, Drysa, Dubna, Aiviekste, Pērse, Dīvaja, Ogre

History
Humans have settled at the mouth of the Daugava and along the shores of the Gulf of Riga for millennia, initially participating in a hunter-gatherer economy and utilizing the waters of the Daugava estuary for fishing and gathering. Beginning around the sixth century CE, Viking explorers crossed the Baltic Sea and entered the Daugava River, navigating upriver into the Baltic interior.

In medieval times, the Daugava was part of the trade route from the Varangians to the Greeks, an important route for the transport of furs from the north and of Byzantine silver from the south. The Riga area, inhabited by the Finnic-speaking Livs, became a key location of settlement and defence of the mouth of the Daugava at least as early as the Middle Ages, as evidenced by the now destroyed fort at Torņakalns on the west bank of the Daugava in present-day Riga. Since the Late Middle Ages, the western part of the Daugava basin has come under the rule of various peoples and states; for example, the Latvian town of Daugavpils variously came under papal, Slavonic, Polish, German, and Russian rule until the restoration of the Latvian independence in 1990 at the end of the Cold War.

Settlements
The following are some of the cities and towns built along the Daugava:

Russia
• Andreapol

• Zapadnaya Dvina

• Velizh

Belarus
• Ruba

• Vitebsk

• Beshankovichy

• Polotsk (home to the Boris stones)

• Navapolatsk

• Dzisna

• Verkhnedvinsk

• Druya

Latvia
• Krāslava

• Daugavpils

• Līvāni

• Jēkabpils

• Pļaviņas

• Aizkraukle

• Jaunjelgava

• Lielvārde

• Kegums

• Ogre

• Ikšķile

• Salaspils

• Riga

Environment
The river began experiencing environmental deterioration in the Soviet era due to collective agriculture (producing considerable adverse water pollution runoff) and hydroelectric power projects. This is the river that the Vula river flows into.

Water quality
Upstream of the Latvian town of Jekabpils, the river's pH has a characteristic value of about 7.8 (slight alkaline). In this area, the concentration of ionic calcium is around 43 milligrams per liter, nitrate is about 0.82 milligrams per liter, ionic phosphate is 0.038 milligrams per liter, and oxygen saturation is 80%. The high nitrate and phosphate load of the Daugava has contributed to the extensive buildup of phytoplankton biomass in the Baltic Sea; the Oder and Vistula rivers also contribute to the high nutrient loading of the Baltic.

In Belarus, water pollution of the Daugava is considered moderately severe, with the chief sources being treated wastewater, fish-farming, and agricultural chemical runoff (such as herbicides, pesticides, nitrates, and phosphates).