Here in East Central Indiana I have a friend that built a dammed pond that was fed partially from a pond run off of an elevated pond of an owner next to him, that intern was fed from another pond across the road. The friends ponds run off fed near the head of a very small stream called White River that intern finally runs into the Ohio River.
I have two fields, corn/soybeans, water can come down after a heavy rain into my field from a neighbor's higher elevation field and cause damage, to my crops where as this water flows through a small culvert under a road into a neighbors field and so on. So the laws of nature are water seeks it's own level. When you are building your pond if you are damming it that might be considered an obstruction of the natural flow of water, but I doubt it, on the other hand if you are just digging a hole I would think you are absolutely free and clear. But of course check with your state.
The flow of water is interesting. In my area almost every farm around is putting in plastic tubing in their fields to run off excess water to enhance their corps. So what happened when we got a big rain in the last few days? All of the square miles of drained land with water flowing all at the same time rose the level of the water trying to get through the open ditches, creeks and rivers and the fields were flooded more then ever from the backup. Like stuffing ten pounds of stuff into a five pound bag.
