The Estuarine Mix.

Where fresh river water meets the salty surge of the tide, a unique chemical environment known as brackish water is born.

Estuaries act as the biological filters of the coastline. Because salt water is denser than fresh water, it often slides underneath the river outflow in a "salt wedge." This stratification creates a complex circulation pattern that traps nutrients and sediments, making estuaries among the most fertile ecosystems on the planet.

The salinity in an estuary is never constant; it fluctuates with the tides and the seasons. Species living here must be euryhaline—capable of adapting to rapid changes in salt concentration. These areas serve as critical buffer zones, protecting the inland from storm surges and filtering pollutants before they reach the open ocean.