Exorheic, or open lakes drain into a river, or other body of water that ultimately drains into the ocean. Endorheic basins fall into the category of endorheic or closed lakes, wherein waters do not drain into the ocean, but are reduced by evaporation, and/or drain into the ground.

No, not all lakes run into the ocean; these exceptions are known as endorheic or "closed" lakes. While most "open" (exorheic) lakes eventually drain into rivers that carry the water to the sea, endorheic lakes are located in basins where there is no outflow to the ocean. Instead, the water level is balanced primarily by evaporation and seepage into the ground. Because minerals and salts are left behind when water evaporates, these closed lakes often become significantly saltier than the ocean over time. Famous examples include the Great Salt Lake in Utah, the Caspian Sea (which is geographically a lake), and the Dead Sea. These basins are typically found in arid or semi-arid regions where the rate of evaporation exceeds the amount of rainfall and river inflow. In contrast, "open" lakes, like the Great Lakes of North America, are constantly being "flushed" out by river systems—such as the St. Lawrence River—which eventually deposit the freshwater into the Atlantic Ocean, maintaining the lake's freshwater status and completing the traditional hydrological cycle.