Endorheic basin

An endorheic basin is like a swimming pool that doesn't have a hole in the bottom. When you jump into the pool, the water doesn't go anywhere because there's no drain for the water to escape. Endorheic basins work the same way but with larger bodies of water on the earth's surface.

Instead of a pool, imagine a big area of land where all the rainwater and streams flow into a low-lying spot. But this spot is surrounded by high mountains or hills that keep the water from flowing out. So the water stays there, making a lake or even a small sea.

Because there's no outlet for the water, the basin tends to become salty over time. That's because the rainwater and streams that flow into it contain minerals and salt that get trapped and concentrate in the water. So these basins can support unique ecosystems and organisms that are able to survive in salty water, but they also become very sensitive to changes in the water's chemistry.

Some famous examples of endorheic basins include the Caspian Sea, the Dead Sea, and the Great Salt Lake in Utah.