The Sultansazligi Wetland, an internationally important aquatic site in Turkey, has suffered from a severe contraction since the early 1990s. To determine the factors affecting contraction, temporal variations of climatic and hydrogeologic variables have been investigated. Both the long-term climate change and the increasing surface and groundwater use are found to be responsible. Hydrologic analyses reveal an apparent correlation between increasing use of water resources and contraction in the wetland. Particularly, increasing use of groundwater and complete capture of springs and effluent streams once feeding the wetland are found to be the prime factors. Furthermore, a strong coherence is found between the temporal trend of the North Atlantic Oscillation and local precipitation, which is the main source of the basin's water excess and supplies the wetland. Future existence of the wetland depends on the application of thrifty water-use polices in irrigation.