Estuarine scientists use many terms to describe the complicated physical processes in estuaries, where freshwater from the rivers mixes with saltwater from the sea. Tidal currents are strongest during full and new moons, called spring tides, and weakest during half moons, called neap tides.
Salinity is greatest near the ocean and smallest near the rivers.
The null zone is the region in the estuary where the residual, near-bottom, landward current reverses and flows in the seaward direction as a result of river inflow.