Upper Colorado River Delta in Gulf of California31.6N 114.7W
An estuary is an inlet, or bay at the mouth of a river or stream, where the salt water from the ocean mixes with fresh water. A positive estuary is one in which the seawater component is diluted; therefore, the water is brackish, with salinity less than that of the ocean. In contrast, a negative estuary is an estuary in which the evaporation of seawater is relatively greater than that of the fresh water input.
In the Gulf of California, there are a number of negative estuaries, which possibly were previously positive. However, due to human modification of the land use around the Gulf of California and water diversion for municipal and agricultural use, there are no longer many rivers that freely empty into the Gulf of California.
The upper Colorado River Delta, visible near the image center, is one example of a historically major estuary and wetlands ecosystem, that since the 20th century construction of upriver dams and diversion aqueducts on the Colorado River, is now a small ephemeral remnant estuary.