The Urmia Lake in NW Iran, the world’s second-largest hypersaline lake, has been exposed to rapid water level fall in the last two decades due to water resources mismanagement, building up of dams on inlet rivers, and the causeway construction in the lake. This human intervention has divided the lake into northern and southern parts and caused an extreme disturbance in the hydro-chemical and hydrodynamic systems, namely current direction reversal. To fully understand the current situation, water depth and lake surface and deepwater physico-chemical parameters (i.e. density, temperature, acidity, electrical conductivity, and total dissolved solids) are analysed in the wet and dry seasons of 2019. In the wet season, deepwaters have a higher density than surface waters, and the northern part of the lake contains denser water compared to its southern counterpart. The formation of density gradients creates an anticlockwise direction lake current. Deepwaters show higher electrical conductivity and total dissolved solids than surface waters in the wet season. Unlike the wet season, the lake water becomes more homogenised due to wave action and evaporation in the dry season. Our study clearly demonstrates that the water passageway of the causeway does not allow for a complete yearly balance between water and sediment exchange. Results suggest that the northern and southern parts of the lake have almost independent hydro-chemical and hydrodynamic systems. In the undeniable reality of global warming trends, anthropogenic interventions into sensible ecologic systems need to be better planned if we were to prevent the ecological disasters we now have to face.

伊朗西北部的乌尔米亚湖是世界第二大高盐湖，由于水资源管理不善、在入水河上修建水坝以及在湖中修建堤道，过去二十年里水位急剧下降。这种人为干预将湖泊分为南北两部分，并对水化学和水动力系统造成了极大的扰动，即水流方向逆转。 为充分了解现状，分析了2019年干湿季的水深和湖面及深水理化参数（即密度、温度、酸度、电导率、总溶解固体）。深水的密度高于地表水，与南部相比，湖北部分的水密度更高。密度梯度的形成产生逆时针方向的湖流。在雨季，深水显示出比地表水更高的电导率和总溶解固体。与雨季不同，由于旱季的波浪作用和蒸发，湖水变得更加均匀。我们的研究清楚地表明，堤道的水道不允许在水和沉积物交换之间实现完全的年度平衡。结果表明，湖的北部和南部具有几乎独立的水化学和水动力系统。在全球变暖趋势不可否认的现实中，如果我们要防止我们现在必须面对的生态灾难，就需要更好地规划对合理生态系统的人为干预。