Rivers carry religious significance in traditions that developed independently on several continents. The consistency is easier to explain than it first appears.
Settlement follows water absolutely
Permanent communities require a reliable water supply, and before engineered distribution that meant proximity to a river, spring or lake.
Consequently the founding stories of a great many settlements involve a watercourse, and the river is present in the tradition from its earliest layer.
What a community depends on completely tends to acquire ritual attention, and the dependence here is more total than for almost any other feature of a landscape.
Rivers behave in ways that invite personification
A river moves under its own power, changes character with the seasons, floods without warning and can be generous or destructive within the same year.
These are the properties of an agent rather than an object, and cultures across the world describe rivers in the vocabulary of persons.
The pattern is not naive. It records an accurate observation that a river is not predictable in the way a hill is, and that living alongside one requires negotiation.
Washing carries symbolic weight everywhere
Physical cleaning is one of the few actions that is universally understood and universally performed, which makes it available as a symbol without explanation.
Purification rites involving water appear across traditions, and the presence of running water in particular is often specified because it carries away rather than accumulating.
The gesture is the same in each case even where the theology differs entirely, which is why observers frequently mistake similar rites for shared belief.
Boundaries and journeys concentrate meaning
Rivers form borders, and crossing one has historically meant leaving one jurisdiction for another with all the significance that carries.
They are also routes, carrying trade, pilgrims and news, so a river connects distant places that would otherwise have no relation.
Both properties make a river a natural setting for rites concerning transition, and crossings appear in the ritual vocabulary of many traditions.
Sacred status has practical consequences today
Rivers venerated by large populations attract enormous ritual use, and that use interacts with pollution, water abstraction and flow regulation in complicated ways that no single authority controls.
Some legal systems have granted rivers forms of legal standing, drawing on both indigenous frameworks and environmental law, so that harm to the river can be pursued in its own name. These experiments are recent, contested and unevenly applied.
Religious attachment cuts both ways here, sustaining conservation campaigns in some places while complicating them in others, and the outcome depends on local circumstances rather than on the tradition itself.