For nearly 500 years preceding 1878, Dobruja was under Turkish rule. When the Turks were forced to relinquish their control, the largest elements of its population were Romanian and Bulgarian, and it was divided between the two countries. Romania received the larger, but more sparsely populated, northern portion. Between the two world wars Romania held the entire area, but in 1940 Bulgaria regained the southern portion. The 1940 boundaries were reconfirmed after World War II, and since then the Romanian portion has had an area of approximately 6,000 square miles; Bulgaria's has been approximately one-half as large. Dobruja contains most of the Danube River delta marshland, much of which is not easily exploited for agricultural purposes, although some of the reeds and natural vegetation have limited commercial value. The delta is a natural wildlife preserve, particularly for waterfowl and is large enough so that many species can be protected. Fishing contributes to the local economy, and 90 percent of the country's catch is taken from the lower Danube and its delta, from Dobruja's lakes, or off the coast. Willows flourish in parts of the delta, and there are a few deciduous forests in the north-central section. To the west and south, the elevations are higher. The land drains satisfactorily and, although the rainfall average is the lowest in the country, it is adequate for dependable grain crops and vineyards. Along the southern one-half of the coastline there are pleasant beaches. In summer the dry sunny weather and low humidity make them attractive tourist resorts. Bukovina, more isolated than other parts of the country, has a part-Romanian and part-Ukrainian population. Romanian Bukovina is small, totaling only about 3,400 square miles. It was part of Moldavia from the fourteenth century until annexed by Austria in 1775. Romania acquired it from Austria-Hungary in 1918, but after World War II the Soviet Union annexed the 2,100-square-mile northern portion with its largely Ukrainian population. The approximately 1,300 square miles of the former province remaining in Romania is picturesque and mountainous. Less than one-third is arable, but domestic animals are kept on hillside pastures and meadows. Steeper slopes are forested. Drainage All of Romania's rivers and streams drain to the Black Sea. Except for the minor streams that rise on the eastern slopes of the hills near the sea and flow directly into it, all join the Danube River. Those flowing southward and southeastward from the Transylvanian Alps drain to the Danube directly. Those flowing northward and eastward from Moldavia and Bukovina reach the Danube by way of the Prut River. Most of the Transylvanian streams draining to the north and west flow to the Tisza River, which joins the Danube in Yugoslavia, north of Belgrade.