Here's why:

* Flooding: The Salton Sea was formed accidentally in 1905 due to flooding from the Colorado River.

* Evaporation: The Salton Sea is a closed basin, meaning there is no outlet for the water to escape. As a result, the water evaporates, leaving behind salt and minerals. This constant evaporation causes the sea to shrink in size significantly.

The Salton Sea's fluctuating size is a major environmental concern, impacting the local ecosystem and human communities.