River Terminology: Source (Headwaters) and Mouth (Where It Empties)

Every river has a beginning and an end, defined by standard hydrological terms:

Source (Headwaters)

The **source** is the furthest point from the mouth where the river begins. It can be:

• Spring: Groundwater emergence (e.g., Mississippi at Lake Itasca).
• Glacier: Meltwater from ice field (e.g., Ganges at Gangotri, Rhone at Rhone Glacier).
• Lake: Outflow from a lake (e.g., Nile at Lake Victoria; Rhine at Lake Toma).
• Confluence: Where two streams merge to form the named river (e.g., Missouri + Mississippi = Mississippi).
• Wetland / Seepage: Diffuse origin in marshy ground.

Often multiple source streams exist; the **longest tributary** defines the "true source" for length measurements.

Mouth

The **mouth** is where the river empties into a larger body of water:

• Ocean / Sea: Delta (Nile, Mississippi, Amazon, Mekong) or estuary (Hudson, Thames, Amazon lower).
• Lake: Tributary inflow (e.g., rivers into Lake Baikal, Great Lakes).
• Another River: Confluence as tributary (e.g., Ohio River into Mississippi at Cairo, IL).
• Inland Sink (Endorheic): Disappears in desert (Okavango → Kalahari; Amu Darya → Aral Sea—historically).

Additional Terms

• Headwaters: Upper reaches, often plural (source streams).
• Confluence: Meeting of two rivers.
• Delta: Sediment fan at mouth (distributaries).
• Estuary: Tidal mouth with freshwater-saltwater mixing.

Source to mouth: the river's longitudinal profile—energy, sediment, life, and human history flowing downhill.