Major threats to pioneer life came from accidents, exhaustion, and disease. Crossing rivers were probably the most dangerous thing pioneers did. Swollen rivers could tip over and drown both people and oxen. Such accidents could cause the loss of life and most or all of valuable supplies. Animals could panic when wading through deep, swift water, causing wagons to overturn. Animals could cause very serious injury to their owners. People could be crushed by wagons or animals, thrown by horses