Fishes Freshwater fish communities change from one hydrographic basin to another, due to the lack of connectivity between watercourses. Most Iberian freshwater fish evolved in isolation from those of the rest of Europe and do not occur anywhere else in the world (Iberian endemisms). Many of them are threatened. Watercourses in the Neves-Corvo region are part of the Guadiana River basin and have unique characteristics due to the region’s climate. The Oeiras stream is the only one that flows all year round. Because of the high temperatures and lack of rain during the summer, all the remaining streams dry completely or are reduced to small water pools. The fish that thrive in them are co-adapted to the high water temperature, which can exceed 45 °C, and to the lack of oxygen. In these summer periods, it is common to observe birds (e.g. white stork) catching the trapped fish. With the arrival of the autumn rain, the rivers flow freely again and the survivors re-populate them. Water pollution, invasive species, the use of water for irrigation and global warming are the main threats for these endemic species.