Lets think about this bass relate to cover and if the cover is gone so will the bass. Find some other type of cover in the canal and I would say you'll find the bass.
As for the dead bass comments, these are all incorrect.
Herbicides were put in a canal, canals are flowing water, so the water quality (dissolved oxygen, pH) would not have been a problem.
Herbicides are strictly regulated by the EPA and only the correct one for the intended application can be used. Herbicides are not just "dumped" in the water. Many measurements are taken to insure the correct amount is being used so that negative impacts (fish kills) to the enviroment are not caused.
Aquatic plant control in canals has to be done when plants reach nuisance levels. The canals were made for water movement just as reservoirs were made for water control (retention, navigation), fishing is just a benefit from both.