Do tornadoes stop at rivers

Tornadoes don't have a particularly significant influence. When tornadoes remove vegetation it may increase runoff and erosion near rives, increasing the amount of water and sediment that enters the river, but this is probably a small contribution. Tornadoes that cross rivers may suck unfortunate fish and other aquatic animals into the air as well. A tornado in Minnesota in 1939 was reported to have momentarily sucked the Mississippi river dry. This, however, was likely an exaggeration.