A river is a natural, flowing watercourse that moves under the influence of gravity, transporting water and sediment from a source to a final destination. This final point, known as the river’s mouth or terminus, is a varied geographical and hydrological feature. The path a river takes is determined by topography, climate, and geology, leading to distinct ways a river’s journey can conclude. Hydrologists classify these termination points into categories that include the widely known flow into the ocean and the less common endings within continental landmasses.
Terminating in the Ocean or Sea
The most common fate for a river is to empty into the ocean or a sea, a process known as exorheic drainage. This termination point is where the river’s freshwater meets the ocean’s saltwater, creating one of two primary coastal formations: a delta or an estuary. Sediment deposition and tidal energy dictate which of these features will form at the river mouth.
A delta forms when a river carries a large volume of sediment and empties into a body of water with low tidal range and weak currents, allowing the sediment to settle. As the river’s current slows drastically upon meeting the sea, the heavy load of clay, silt, and sand is deposited, creating new land. This process causes the main river channel to split into numerous smaller waterways called distributaries, forming a fan or bird-foot shape, such as the vast delta created by the Mississippi River. The Nile River Delta in Egypt is another classic example, where the river’s sediment built a massive, fertile triangular plain.
Conversely, an estuary is a partially enclosed coastal body of water where the river’s freshwater is mixed with the ocean’s saltwater. These mouths often form in regions where the land has subsided or where the river valley was carved by a glacier, resulting in a deep, funnel-shaped channel. The strong tidal currents in an estuary prevent the massive buildup of sediment that characterizes a delta, instead scouring the channel and keeping it deep. The Amazon River forms an enormous estuary rather than a true delta due to the powerful ocean currents and tides that sweep the material away.
Flowing into Inland Water Bodies
Not all rivers complete their journey to the ocean; many terminate within the continental interior by flowing into a large, permanent body of water. These inland terminations include natural lakes and man-made reservoirs, which serve as the final collecting points for their drainage basins. In these cases, the river channel ceases to exist as a distinct, flowing entity, and its water becomes part of the larger standing body.
Some rivers flow into large, freshwater lakes that themselves have an outlet to the ocean, such as the numerous rivers feeding the Great Lakes in North America. These rivers are still technically part of the ocean’s overall drainage system, but their immediate termination is the lake. Other rivers flow into lakes that have no outlet, known as terminal lakes, where the water is only lost through evaporation. The Volga River, Europe’s longest river, flows into the Caspian Sea, which is the world’s largest terminal lake.
The Jordan River provides another example, flowing into the Dead Sea, which is one of the lowest points on Earth and a hypersaline terminal lake. Water flowing into these closed basins accumulates dissolved minerals over time, making them increasingly salty as the water evaporates. Humans also create inland terminations through the construction of vast reservoirs for water storage, flood control, and power generation. When a river flows directly into one of these large impoundments, the river’s natural course effectively ends at the reservoir’s headwaters.
Ending on Land
The most complex river endings occur when the water disappears entirely into the land before reaching any large, permanent body of water. This happens primarily in closed drainage systems, or endorheic basins, where the geography traps the water internally. In these arid and semi-arid regions, the water loss mechanisms of evaporation and infiltration dominate the river’s final fate.
Many rivers in endorheic basins flow into terminal lakes that are temporary or highly seasonal, often becoming dry salt flats, or playas, during drier periods. The Great Salt Lake in Utah sits within the largest endorheic basin in the Americas, and its source rivers flow into it, where the water is entirely lost to evaporation. The water in these systems does not flow to an external sea, leaving the minerals to concentrate and create the characteristic saline environment.
A river can also “disappear” through a process called infiltration, where the water soaks into the ground and becomes groundwater. This often occurs in porous geological regions, such as karst landscapes with limestone, or in desert regions where the river crosses a sandy plain. The Humboldt River in Nevada is a classic example of a lost river, whose flow eventually dissipates into the dry, porous soil of the Humboldt Sink.
A related phenomenon is the formation of an inland delta, a vast, fan-shaped wetland where the river’s flow spreads out and is consumed by evaporation and plant uptake. The Okavango River in southern Africa never reaches the sea, instead fanning out into the Okavango Delta, a massive, dynamic wetland within the Kalahari Desert. The river’s entire volume is lost through evapotranspiration and infiltration into the sands, providing a unique terrestrial end to its long aquatic journey.