Lake Neusiedl, or Fertő, is the largest endorheic lake in Central Europe, straddling the Austrian–Hungarian border. The lake covers 315 km2 (122 sq mi), of which 240 km2 (93 sq mi) is on the Austrian side and 75 km2 (29 sq mi) on the Hungarian side. The lake's drainage basin has an area of about 1,120 km2 (430 sq mi). From north to south, the lake is about 36 km (22 mi) long, and it is between 6 km and 12 km wide from east to west. On average, the lake's surface is 115.45 m (378.8 ft) above the Adriatic Sea and the lake is no more than 1.8 m deep.

An endorheic basin is a drainage basin that normally retains water and allows no outflow to other, external bodies of water ; instead, the water drainage flows into permanent and seasonal lakes and swamps that equilibrate through evaporation. Endorheic basins are also called closed basins, terminal basins, and internal drainage systems.