A tidal river is a river whose flow and level are influenced by tides. A section of a larger river affected by the tides is a tidal reach, although it may sometimes be considered a tidal river if it has been given a separate name. The Brisbane River, which flows into the Pacific Ocean from the east coast of Australia, is also a tidal river.
Generally, tidal rivers are short rivers with relatively low discharge rates but high overall discharge; generally this implies a shallow river with a large coastal mouth. In some cases, high tides impound downstream flowing freshwater, reversing the flow and increasing the water level of the lower section of river, forming large estuaries. High tides can be noticed as far as 100 kilometres (62 mi) upstream. The Coquille River is one such stream where this effect can be noticed.