This game compares published river lengths, usually in kilometers from source to mouth.

• A longer river is not automatically a bigger river by water volume or basin area.
• Length sounds simple until tributaries, headwater definitions, and measurement conventions enter the room.
• Some entries are tributaries listed in reference tables, which is why famous basins can appear more than once through different channels.

River length is one of those statistics that looks settled until you ask exactly where the river begins.