Continuity mistake: After Dinky tells Big Mama and Boomer his idea, when Boomer flies over to Widow Tweed's house to knock on the front door, the water pump is beside the tree at the left side of the house, but when Widow Tweed opens the door and hurries over to the "pesky" birds, the water pump is now at the right side of the house. It continues to change its position in front of the house in following shots. (00:07:50)
Answer: He fell into the water so he could have very easily broken his leg on something in the water like a rock.