In Nebraska, no matter how large my pond is, or how much I spent on it, the landowner who is higher on the watershed can build any pond he wants. The only restrictions would be that a permit is necessary for any pond that will hold more than 15 acre-feet of water.
The only way to tell if it will affect your pond is to do an analysis of watershed size, soil permeabilities, soil slopes and annual precipitation. This could tell you if there is enough flow-through on the pond above to keep your pond adequately supplied.
In some cases it's no problem, in other cases it's a deal breaker. Actually in some cases it could even be an advantage if you had a relatively large watershed and you could let your neighbor collect all of your silt for you.
