Bert, I have disagree the GLY-4 is harmless to fish. Madison county, AL district one sprayed the roadsides heavy right before a heavy rain. It washed into the creeks and rivers in the area. A few week the fish in one river that I fished had massive sores on their bodies and were dying along with most the plant life along the river. ON of course the same district spray directly over over the water where I was fishing one time and I crawled them about it. They said didn't spray across water but pictures don't lie as showed them the pictures. They corrected they spraying habits afterwards.
Some notes on 2,4-D. It is highly volatile especially the ester version so it must be applied only when the temps are below 80F on low humidity days. It gases off; therefore, drifts acoss nearly plantings as it is a heavy vapor and can/will damage desirable plants (especially farm crops). The amine version is less volatile but same cautions apply.
Side note several of the plants shown are actually editable. And the clover is one source of nectar bees use to make honey.
Glyco is harmless to anything other than green plants
The burning question is what else was mixed in with it .
Very common to add surficants & wetting agents ,
These can cause damage to fish but strait glyco as in Round Up or Zero as sold retail in Australia will not harm fish other than killing aquatic plants
However being in the USA where rivers are treated like sewers and disposal of hazardious chemical does not seem to be controlled I would hazard a guess that what you observed happening was more likely a tanker discharging toxic waste into the river upstream rather than taking it to a hazardous liquid waste disposal center and paying a fortune to dump it .
We got smart decades ago and now every drop of toxic liquid waste has to be accounted for from the time it is made till the time it is destroyed .
Glyco works by blocking a specific enzime pathway and those enzimes are only found in plants which includes some forms of alge
Like anti-biotics, idiots apply way too much at way too high a concentration .
Glyco is very long lived which has been a worry as it has been found to wash out of crops that were sprayed several months earlier after heavy rain
This is the major problem in that it can only be adsorbed through the leaves so what does not get adsorbed accumulates in the soils then get washed out into rivers when it rains
Just because the road is wet it does not meant that it has been raining .
People hate Monsanto ( for good reasons ) so are always trying to get at them by finding an adverse effect of glyco so Monsanto can be sued out of existance
To date the closest any one has come was a finding that there was a possibillity that round up may be connected to non-Hodkins lymphoma because 300 people with this cancer all had trace amounts of Glyco in their bodies .
They also had several thousand other man made chemicals as well but the lab only reported on the glyco
They published a report that said there was a possibility that there may be a connection between the cancer and glyco .
This was enough to allow a Californian court to decide that a groundsman with advanced lymphoma could sue Monsanto when he actually had been misusing the product on the grounds of a school for decades and if any one should have been sued it was the school for not ensuring he was following the OH & S protocols for use of Glyco but of course the school had no money so they sued Monsanto instead