Estonia is the most northerly of the three Baltic Republics. Together with Latvia and Lithuania they form the Baltic States. The country is bordered by the Baltic Sea to the north and west, by the Gulf of Finland to the north, by the Russian Federation to the east, and by Latvia to the south. The landscape of Estonia is mainly made up of low-lying plains. There are some hills in the central and the southern regions. Nearly a half of the terrain of Estonia is covered by forests. The longest river of Estonia is Pärnu. The geographical position of the country influences its climate. The closeness of the Baltic Sea makes the climate moderate with cool summers and cold winters.