of flooding for settlements located in the Chu Valley. In the winter of 1878, an ice gorge formed on the Chu River upstream from Tokmok, the administrative centre of Semirechye Province. This was followed by severe flooding that damaged the town and the province's capital was moved to Pishpek (Bishkek). Dams The river flow is regulated by the dam at Orto-Tokoy Reservoir in Kyrgyzstan built in 1957 and the dam at Tasotkel Reservoir in Kazakhstan built in 1974. Ecology and environment Environmental monitoring The Kyrgyz State Agency for Hydrometeorology and the Kazakhstan Hydrometeorological Service (Kazhydromet) operate a number of water quality monitoring stations on the Chu River and its tributaries. Water quality According to the Kyrgyz State Agency for Hydrometeorology, in 2004–08 the water pollution index of the Chu River in the Chu Valley ranged from 0.25 to 0.7 units, which is interpreted as Class II ("Clean water"). The only exception was a monitoring point downstream of Vasilyevka village where the water pollution index ranged from 0.4 to 1.2 units and water quality was assessed as Class II(Clean)/Class III ("Moderately polluted"). According to the Kazakhstan Hydrometeorological Service (Kazhydromet), the water pollution index of the Shu (Chu) River in the Jambyl Region of Kazakhstan amounted to 2.01 (Class III, "Moderately polluted") in 2008, and 1.83 (Class III, "Moderately polluted") in 2009. Such water quality parameters as biochemical oxygen demand, nitrites, copper, and phenols exceeded the maximum allowable concentrations. Major tributaries In Kyrgyzstan, 4892 rivers and canals flow into Chu River. The main tributaries are, from source to mouth: Kochkor (left) Joon Aryk (right) Chong-Kemin (right) Kichi-Kemin (right) Kara-Konguz (right) Shamshy (left) Ysyk-Ata (left) Alamüdün (left) Ala-Archa (left) Jylamysh (left) Kakpatas (right) Ak-Suu (left) Kuragaty (left) Gallery See also Chu-Ili Range References