Looks like glyphosate with an aquatic-life safe surfactant is OK. Some use ROund-Up, despite possible problems it may cause frogs. "Rodeo" may be the best to use.

Source/References:

Weeds
Unwanted Bullrushes
Similar situation with alternative control methods


"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
[Linked Image from i.pinimg.com]