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Within the Helsinki Commission PLC-3 Programme for Estimation of Pollution Load from Coastal Zone into the Baltic Sea, hydrochemical water quality parameters are measured at sampling points in the lower reaches of the rivers Gauja, Salaca, Daugava, Lielupe and Venta.
Oxygen conditions are generally satisfactory. Biological oxygen demand (BOD) and chemical oxygen demand (COD) are parameters indicating the levels of organic pollution in surface waters. The BOD values exceed EU standards most often in the Salaca River (12%) and Lielupe River (10%) catchment areas. According to the BOD values, Latvian river basin waters mainly correspond to a water quality level of I-II.
Source: Latvian State Hydrometeorological Agency
Trend analysis of the main hydrochemical water quality parameters since 1995 do not show a significant improvement of water quality in the larger Latvian rivers.
Source: Latvian State Hydrometeorological Agency
During the last 5 years (1992 - 1997), the contamination of the Daugava River basin with oil products has decreased.
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Biological Quality in Latvian Small Rivers
The biological quality of 527 small rivers was studied during 1993-1997. The survey showed 21% of the rivers to be clean to insignificantly polluted, 64% were insignificantly polluted, 11% were insignificantly polluted to polluted, and 4% were polluted. The small rivers typical had insignificantly polluted river spans. Consequently, the biological quality of about 85% of the investigated rivers is satisfactory.
Lake Water Quality
There is no comprehensive study on lake water quality in Latvia. The largest lakes in the vicinity of Riga are very important both for the water supply in Riga and for recreational purposes. Due to waste water discharge, the most part of them now are typical eutrophic lakes.
Lakes Engure and Kanieris are lakes of the List of Wetlands of International Importance, Especially as Waterfowl Habitat. Lakes Engure is one of the largest shallow coastal lakes in Latvia. The hydrochemical conditions there are stable, and the concentrations of nutrients, BOD and COD correspond to the class of insignificantly eutrophic lakes. Lake Kanieris also belongs to eutrophic.
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