I didn't realize you intended to dam the stream. Please disregard my comment above.
When damming a stream, it is very easy to impound water beyond the boundary of your property. Especially when you are dealing with bedrock and cannot excavate to achieve part of your depth.
In the flat parts of Kansas we have streams with a slope of only 5' per mile. Obviously, if you build a dam 5' tall, then you will back up water for an entire mile!
I am sure the slope of the stream is MUCH higher at your property. However, if you build a dam 14' above the bedrock (plus the freeboard safety margin), examine your topographic map very carefully to make sure the water does not go beyond your property line and the edge of the two neighbors' property that you are adding to your project.
Further, you do have experts above giving you advice about permitting. However, every state has their own specific laws about constructing ponds and impounding water in creeks. You need to use the good "general" advice to make sure you ask the right questions for your state - and eventually go through the correct agencies. Then there are also some federal regulations that may also apply.
I will say, that it is much easier to build a pond in a place and manner such that the Corps of Engineers does not have any jurisdiction. Damming a creek is much more likely to bring your project under their purview.
