Tall reeds are a location on a lake, river, or wetland where reeds or tall grasses grow in abundance. These may be concentrated on the shore of the body of water, or if the water is shallow, they may be growing throughout it. There may be channels through the reeds that allow for boat travel. If the reeds are particularly tall, especially in fantasy worlds, these channels may be more like tunnels through the dense plant-life and the reeds may function more like a fictional grass sea.