The hydrographic network

The climate conditions and relief of the region have caused formation of numerous small inland water bodies in the territory of Estonia. Annual precipitation here exceeds evapotranspiration and the excess water (200–300 mm/year) runs off via rivers. The territory is divided into four basins: the drainage basin of Lake Peipsi (38%), the drainage basin of the Gulf of Finland (excl. the Narva River; 21%), the Gulf of Riga (32%) and the islands of West-Estonia (9%). The most important watershed area in the region is Pandivere Upland.

There are many rivers in Estonia, the majority of which are short and have a relatively small runoff. In dry summers, some of the rivers may temporarily dry out. During spring floods, however, large areas may be flooded (flooded areas of the Emajõgi River, Riisa and Kasari are well-known). Only ten rivers are longer than 100 km. The river with the largest runoff in Estonia is the Narva River. The Narva River receives its water from Lake Peipsi and flows into the Gulf of Finland. The Emajõgi River, which has a very low flow velocity, connects the two largest lakes in Estonia — Lake Peipsi and Lake Võrtsjärv. The Emajõgi River is the only river in Estonia which is navigable over its whole length (101 km). The longest river in the central part of Estonia is the Pärnu River (144 km). For Tallinn, the capital of Estonia, the Pirita River is of utmost importance as its water is discharged via a canal into Lake Ülemiste, which supplies Tallinn with municipal water. Of the rivers of Southeast Estonia, the Ahja and Võhandu rivers are well-known for their deep beautiful valleys with Devonian sandstone outcrops.

In the territory of Estonia there are about 1200 natural lakes whose water area exceeds 1 ha. Lakes cover 4.7% of the territory of Estonia and are unevenly distributed over the territory. As the majority of lake basins formed during the melting of continental ice, the areas abounding in lakes remain mostly in the regions with varied relief. Many of them are located in the uplands of South Estonia (Haanja, Otepää, Sakala, and Karula) and in Vooremaa, with only a few in Pandivere. Well-known lake groups in the northern part of the territory of Estonia are located in Alutaguse (Kurtna lake system) and in North-Kõrvemaa (Aegviidu, Jussi lake systems). On the low coasts of the mainland of West-Estonia and on the coasts of Hiiumaa and Saaremaa islands, a large number of coastal lakes can be seen which have formed, due to surface uplift, in the areas of former bays. In mires, bog lakes can be seen in peaty earth. The number of bog pools (ca 20 000), however, is much larger: most of these have not been registered as lakes. Only Lake Peipsi and Lake Võrtsjärv can be classified as large lakes, and all the other lakes are small lakes (of these only 42 are larger than 1 km2). Most of the lakes are shallow and only approximately 20 of them are deeper than 20 m. Lake Rõuge Suurjärv is the deepest (38 m).

Creation of artificial water bodies, mainly to ensure operation of water mills, has been relatively common in Estonia throughout the centuries. To date, approximately 150 such artificial lakes have been preserved. In order to diversify landscapes and create swimming possibilities, new artificial lakes have been constructed in the vicinity of large settlements. The largest artificial lake is the Narva Water Reservoir at the Narva River. The total area of the reservoir is 200 km² of which 40 km² is located in the territory of Estonia. In order to ensure a water supply to the population of Tallinn, water reservoirs have been constructed at the Pirita, Jägala and Soodla rivers.

Estonia is famous for its beautiful springs. The largest of them are Roosna-Alliku, Esna, Prandi, Varangu and Simuna (located in Pandivere Upland or at the foot of Pandivere Upland), the discharge of which is several hundreds of litres per second. Although, the total number of springs in Estonia exceeds 5000, most of them are small and may temporarily dry out. The water in the lakes with several underwater springs is transparent and cold (Äntu lakes, Lake Sinialliku in Viljandi county, some Rõuge lakes). The distribution of springs also strongly influenced the development of settlements. As springs ensured a water supply to the local population, farms, villages and manor houses were constructed, if possible, not far from springs.

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