Perhaps the most remarkable feature of the country is the presence of numerous important lakes. The Lake of Shkodër is the largest lake in Southern Europe and located in northwest. In the southeast rises the Lake of Ohrid that is one of the oldest continuously existing lakes in the world. Farther south extends the Large and Small Lake of Prespa, which are among the highest positioned lakes in the Balkans. Rivers rise mostly in the east of Albania and discharge into the Adriatic Sea but as well as into the Ionian Sea to a lesser extent. The longest river in the country, measured from its mouth to its source, is the Drin that starts at the confluence of its two headwaters, the Black and White Drin. Of particular concern is the Vjosë, which represents one of the last intact large river systems in Europe.