Herbicide for Himilayan Balsam near stream

[RBudd]

I have a serious infestation of himilayan balsam growing along a stream to deal with. For the most part I've used triclopyr weedkillers around pasture, but I gather they're not appropriate around waterways. Could anyone suggest something that would deal with it well, preferably not kill off all the grasses, and be safe for use near waterways?