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Drużno ((ポーランド語:Jezioro Druzno); (ドイツ語:Drausensee), (リトアニア語:Drūsuo)) is a body of water historically considered a lake in northern Poland on the east side of the Vistula delta, near the city of Elbląg. As it is currently not deep enough to qualify as a lake hydrologically and receives some periodic inflow of sea water from the Vistula Lagoon along the Elbląg River, some suggest that it be termed an estuary reservoir. A village of recent origin also called Drużno is situated near the lake. The German name ''Draussensee'', in earlier records called ''Drusensee'', is connected to the ancient trade city of Truso, which stood within the lands now occupied by Elbląg. The lake is greatly reduced from its original size partly due to large building expansion of housing in the last few decades, but mainly because of the natural death of the lake by sedimentation. The lake is the site of a nature reserve, one of the 13 sites in Poland protected under the Ramsar convention. ==Geography== The central coordinates of the lake are . It lies to the east of the Nogat, the main right branch of the lower Vistula, at the edge of the lowland of the delta (Żuławy Wiślane), which is a region of shifting sediments and channels partly controlled by dikes, dams and ditches, about . in area and sometimes up to below sea level. The delta ends at Elbląg upland (Wysoczyzna Elbląska), much of which is wooded. The delta itself is sparsely populated, despite the presence of large cities nearby (Gdańsk, Elblag and others). Most of it is rich agricultural land and the rest is a wildlife habitat of great natural beauty. The lake today is a . body of water with a mean depth of about and a maximum depth of . The lake is drained by the Elbląg River. There is only a difference in altitude between the lake and Elbląska Bay, which projects from Vistula Lagoon. The surface altitude of these bodies varies for a few reasons, such as wind. When there is a strong wind blowing to the south the bay can be a meter or so higher than the lake, which causes back currents in the river. The Prussians called Vistula Lagoon by the name "fresh-water bay", which it was in those days. Since then the greatly diminished egress of Vistula water, due to human uses, has brought Baltic water into the bay, now brackish. As a result back currents in the river bring intrusions of brackish water into the lake. Generally the southern end remains fresh. There probably always were reversals of river current, which must have speeded traffic between Frisches Haff and the lake. The lake is surrounded by and includes marsh, swamp and alder thickets. On its surface are floating Nymphaea, submerged are Potamogeton and the marshes feature tracts of Phragmites. It should have sedimented over long ago but the high throughput of water from various sources brings fresh Oxygen into the lake, retarding its aging. Twelve streams empty into the lake radially, with water from another twelve canals being pumped into it. They bring about into the lake (1970) with about 7 draining through the river (1975). Variability in these figures as well as wind and back currents cause expansion and contraction of the lake over wide areas. The total capacity is about with a catchment area of . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Drużno」の詳細全文を読む スポンサード リンク
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