Look anything like this?
Fluridone is what I used but as outdoorlivin247 said, be sure you have the right conditions for it's use. For me, I would almost pay extra for how well it worked,,,,,,
almost 
Here's 5 weeks after the Fluridone treatment:
I tried the manual removal using a "prickly rope" to try and remove it but my pond is just too big and like you said, I couldn't even put a dent in it. On top of that, was told I could remove 80% of it to have it all return within 2 weeks. It reproduces VERY quickly!
There's a lot of information on Fluridone, how it works, benefits, drawbacks, etc. Be sure it's the right product as it's nearly a complete vegetation killer (depending on ppb application rate), yet has no effect on FA.
Good luck and I hope some of this helps.
Keith
*EDITED* - As far as applying it, just be sure you get it below the DW into the water. It does not work on surface-contact! Other than that just get it wet and it will evenly disperse throughout the BOW. You can also expect 45 to 90 days to see complete results.
(I really hope I said all that right)
