I understand that if you want to extend a lake or a river that you have to drain it. Although that isn't as realistic as it sounds. However, having already had water in a river or lake and draining it so that you can extend the river or lake and come to find that water can't be placed back into the river or lake is a major problem. I shouldn't have to dig the previous trench even deeper in order to place water back into the lake or river.