The ordinary properties of rivers (especially named rivers), whether as territorial boundaries, defensive lines or trade/transport routes, tend to be echoed on a deeper level in fantasy. Here the boundary may be between Good and Evil; the defence may be against Thinning or incursion by a Dark Lord – Anduin, the Great River, is a significant line of defence in J R R Tolkien's The Lord of the Rings (1954-1955) – or by Witches, who traditionally cannot cross running water except in a boat made of eggshell. Rivers may be barometers of the Land through which they flow, a diseased river indicating a general need for Healing. Their age and continuity of flow indicate the ancient nature of the land's Story (>>> Time Abyss). Subterranean rivers like Alph in Xanadu (>>> Samuel Taylor Coleridge) have a special resonance, as does the Thames in London and the Rhine in Richard Wagner's Ring cycle.
The liquid in a fantasy river may have any property of a Potion. Notoriously, the river Lethe brings Amnesia, and the name of the Fountain of Youth is self-explanatory. An oddity of magical ecology in Piers Anthony's A Spell for Chameleon (1977) is a barren river wishing to restock itself: drinking its water brings Transformation into a fish. What flows in some rivers may be not water but Stars, souls, the stuff of Magic, or – as with Hell's river Phlegethon – boiling blood. Rivers may contain tutelary Gods, as encountered in C S Lewis's Prince Caspian (1951) and Gene Wolfe's Solder of the Mist (1986); other denizens may include Dragons, Selkies, and nymphs or naiads who may or may not be perilous, like the Lorelei (> Mermaids; Sirens). Travelling along or across any important river may mean a change of condition more significant than movement on the Map: by crossing a mere brook, Alice in Lewis Carroll's Through the Looking-Glass (1871) becomes a queen. [CB/DRL]