Pond drainage advice please

Hi all
This year I decided to extend my existing pond. I added a curved stream to attach the old pond and the newer pond together. Unfortunately the stream appears to be causing both ponds to drain.
The liner from the stream goes into both ponds. I've joined with pond liner tape.
I'm thinking of creating a damn at each end of the stream as both ponds would hold their water separate.
I'm just not sure why the stream keeps draining.
Any thoughts would be greatly appreciated

 

The liner would need to lap well under the top pond liner and well over the bottom pond liner.

 

I agree with Pete. The thing is that there needs to be a significant difference in height between the two ponds so that a ‘fall’ is achieved from one to the other.

 

Good point @Freddy , I was assuming it was like a waterfall, hadn't considered it might be two ponds on a similar level.