«Rivers», sometimes referred to as «Four Rivers», «Shisen» or «Shisen-Sho», is a tile-based game which uses Mahjong tiles.
The aim of the game is to remove all tiles from the board. Only two matching tiles can be removed at a time. Two tiles can be removed if they can be connected by up to three horizontal or vertical lines which pass only through empty spaces. The game is over if future moves are not possible and tiles are left on the board, or the player successfully removes all the tiles.