One response to the suggestion that an herbicide be used to control aquatic weed problems in water is concern that the treatment will reduce the dissolved oxygen content of the water, with possible adverse effects on fish and other aquatic biota.  In fact, some herbicide formulations even have warnings on their label to only treat one-half of a pond.  However, a recent study on treating water hyacinth (Eichhornia crassipes) in the Sacramento-San Joaquin River Delta demonstrates that a decrease in dissolve oxygen is not necessarily the outcome after an herbicide treatment.

Study sites were selected based on sites with water hyacinth growing along channels, and sites in which the water hyacinth grew in sloughs...

Here's something from the Aquatic Plant Management Society blog :: posted Feb. 2017
(Original source: East County Today)

DBW Begins Herbicide Treatment in the Delta for Water Hyacinth and Egeria...