A more thorough explanation:

Alvei mutatio (al-vee-I myoo-tay-shee-oh) is a Latin term that refers to a change in the course of a stream or river.

One example of alvei mutatio is when a river changes its course due to erosion or other natural causes. For instance, the Mississippi River has changed its course many times over the centuries, creating new channels and leaving old ones behind.

Another example is when humans alter the course of a river for various reasons, such as to prevent flooding or to create new waterways for transportation. The Panama Canal, for example, was built to connect the Atlantic and Pacific Oceans by cutting through the isthmus of Panama and changing the course of the Chagres River.

The examples illustrate how alvei mutatio refers to a change in the course of a stream or river. In both cases, the natural or human-induced alteration of the river's path results in a new channel or waterway that may have different characteristics and impacts on the surrounding environment and communities.