Kymi (river)
The Kymi (, ) is a river in Finland. It begins at Lake Päijänne, flows through the provinces of Päijänne Tavastia, Uusimaa and Kymenlaakso and discharges into the Gulf of Finland. The river passes the towns of Heinola and Kouvola. The town of Kotka is located on the river delta. The length of the river is , but its drainage basin of extends to almost inside the Tavastia, Central Finland, Savonia and Ostrobothnia. The furthest source of the river is Lake Pielavesi, its furthest point being some from the sea measured by flow route. The name of the river, itself, "kymi , means large river", in Old Finnish. Being one of the largest rivers in Southern Finland, the Kymi is a major source of hydroelectricity. The towns of Kotka, Kuusankoski, Myllykoski and Inkeroinen along the river are major centres of the pulp and paper industry. Formerly the river was extensively used for timber rafting. The Kymijoki river has five mouths. It divides into two main branches near the Kultaankoski rapids in Kotka, about inland of the Gulf of Finland. The eastern branch splits into the Korkeakoski and Koivukoski branches, the latter branch dividing again to form two mouths (Langinkoski and Huumanhaara). The  Korkeakoski branch has only one river mouth. The western branch divides into Ahvenkoski and Klåsarö branches, each with one mouth. The westernmost Ahvenkoski branch of the river served as a border between Sweden and Russia from 1743 to 1809. The parts of Finland east of the river were later called Old Finland. Old Finland was incorporated in the Grand Duchy of Finland in 1812. The Kymi is very swift: it takes three days for its waters to run from lake Pyhäjärvi to sea. Its mean depth is , and the deepest place is . Hydroelectric plants and rapids. In Kymijoki, there are  12 hydroelectric plants and several dams to regulate the water level. The first power plants were built is 1882. The canal and dam at Kalkkinen is used to regulate the water level of Lake Päijänne. The Hirvivuolle Dam regulates water flow between eastern and western branches. The Paaskoski Dam near Tammijärvi regulates the flow into the Klåsarö branch and the Strömfors Dam regulates the water level of the Strömfors industrial area. Upper and middle reaches: Western branch: Eastern branch: