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Surface water and groundwater resources
Estonia can be divided into four natural river basin districts: Narva-Peipus, the Gulf of Finland, the Gulf of Riga, and the islands. Most of the rivers of the mainland originate on the slopes of the extensive karst area of Pandivere upland (MoE, 2015b).
There are 7 000 rivers, brooks, and canals in Estonia. The river system is thus dense, but most rivers are characterized by short lengths, small catchment areas, and low flow rates. As many as 90 percent of the rivers are up to 10 km long and only 1 percent are over 50 km in length. Only 10 rivers are longer than 100 km. The longest one is the Võhandu river (162 km), followed by the Pärnu river (144 km), and then the Põltsamaa, Pedja, Kasari, Keila and Jägala rivers. The Narva river is the river with the highest discharge. The catchment area of the Emajõgi river covers 22 percent of the country (MoE, 2015b).
Due to karstic features in North Estonia and islands, some rivers flow partly underground (Jõelähtme, Tuhala, Kuivajõgi and others) (MoE, 2015b).
The internal renewable surface water resources (IRSWR) are estimated at 11 712 million m³/year. A total quantity of about 96 million m³/year is estimated to flow from Latvia and the Russian Federation into Estonia. Therefore, the total RSWR are estimated at 11 808 million m³/year (Table 2). An estimated 96 million m³/year flow from Estonia into Latvia and the Russian Federation.
Estonia is rich in groundwater resources. The internal renewable groundwater resources are estimated at 4 000 million m³/year. The main recharge area is in the Pandivere uplands, where limestone areas and sand/gravel ridges are locally important. Generally, in southern Estonia the groundwater of the Devonian aquifer is used, while in western and sporadically in central Estonia the water of the Silurian-Ordovician horizon is used. Part of the groundwater flows out to the sea and part returns to the surface water system. This latter part, which is already accounted for in the runoff (overlap), has been estimated at 3 000 million m³/year, which brings the total renewable water resources to 12 808 million m³ (11 808+4 000-3 000) (Table 3).
Total wastewater produced in 2009 was 385 million m³, of which 307 million m³ was treated.
Lakes and dams
There are over 1 400 natural and human-made lakes, covering 6 percent of the country (Climate Adaptation, 2015b). Lake Peipus at the border with the Russian Federation and lake Võrtsjärv in the south of the country are among the largest lakes in Europe and are nationally monitored lakes, together with Nohipalu Black Lake, Nohipalu White Lake, Pühajärv, Rõuge Big Lake, Lake Uljaste, Viitna Long Lake, Lake Ähijärv, and Mullutu Suurlaht (MoE, 2015b).
The artificial Lake Narva in the Narva river in the northeast was created in 1956, when the Narva hydropower plant started operating. The reservoir is shared by the Russian Federation and Estonia, with a total area of 191 km² and a total capacity of 365 million m³. It provides water to Narva Hydroelectric Station located on the Russian side and cooling water to the Estonian Narva Power Plants. Its average depth is 1.8 m, its deepest point 15 m.