I'm having the same problem with our river. The weeds are just taking over. Someone please give us a solution.

I don't have a solution, sorry, but have you tried contacting your country, state, or county's ag center? You might want to start here:

http://www.csrees.usda.gov/

and here:

http://www.ansi.okstate.edu/internet/Agexten.html

Good luck! =)

I have gone in mine a couple times a year and pulled the weeds out by hand. There's a lot of grass that comes up easily; its just messy. Cattails are another story; very tough, but I'm leaving some since I learned what a benefit they are. There are lots of them on the other side, which is just an area let go and the birds love it.

We can't use any type of machine as there is rock all along the bottom and the banks.

The forget me not type flowers are probably impatiens capensis. It likes to grow in creeks and is a desirable native flower. Great for hummingbirds. It does get "aggressive" in creek beds. But its not harmful.

I would leave them alone. The plants growing in the creek help stabilize the surrounding soil and prevent erosion. If the creeks needs more space for flow, it will knock those plants over, itself.

On our local PBS show this weekend they talked about weeds in creeks. I know you are in Canada and the rules are different but destroying stream banks is apparently a state and federal offense.

Has it flowered yet? If so, is it perchance a pretty magenta-purple? If it's a grass, then it might be Reed Canary Grass (Phalaris arundinacea).

Here is a link that might be useful: Purple Loosestrife