You have to be careful with plants in shallow water like that. As I'm sure you're aware, water plants grow really fast, and the problem with such shallow water is that the roots are going to grow outside the edge of your stream/fall and wick water out of the pond.

It's a natural process for the roots to seek out the soil surrounding your pond, which can cause real problems.

One year I had to go on a massive hunt for why my pond was losing water too fast. After moving many rocks, I finally found the water celery roots that had escaped the stream! I never planted the stream again.