A river is one of the six types of water in Animal Crossing, the others being the ocean, the river pool, the pond, and the waterfall. They stretch from one side of the town and empty into the ocean at the other. A river begins as a waterfall at an edge of town and passes through the town. In some towns, a river flows through a river pool, and may split in two in some towns. There are usually two or three bridges crossing a river. Fish can be caught in a river.
The river mouth is the area where the river meets the ocean. Some fish can be caught only in this particular spot. In some towns, there may be two or more of these, increasing the chances of catching these fish.