The tidewater estuary I grew up on in MD had chemicals dumped in it (over protests) to eliminate aquatic vegetation in one small bay because 'it fouled boat props'.
That was in the 1960s.
Being a tidewater (brackish water) estuary, the chemicals did not just 'run out' but were distributed throughout the entire estuary during subsequent tide cycles.
The vegetation went away, as advertised, and not just in that small bay, but the entire estuary (20 miles long, 2 wide, and tributaries) and with it, so did the fisheries that depended on the animals (crabs and fish) that that vegetation sheltered during critical moments in their life cycles. Those fisheries were worth millions of dollars then, in the '60s, when oysters were $4 a bushel.
In the absence of that vegetation, cow nosed ray schools made incursions and wiped out an entire commercial species of clam (I know what they were eating, we caught one and dissected it on our picnic table, and I personally examined the stomach contents).
In the storms which came after the aquatic vegetation was eliminated, there was nothing to dampen wave energy, so coastal erosion increased, as did sediment and turbidity, and oyster bars were silted out.
Now, most of my lifetime later, the vegetation has not been reestablished, and attempts to move some in have been met with failure. Apparently the plants will grow a little, then die. I'd hypothesize there is a layer down in the bottom that contains enough of the herbicides from then to still kill aquatic vegetation, at least the type that roots in the bottom.
Don't let these people experiment with anything that may have far-reaching and unforeseen consequences. Like I said, build a saltwater aquarium, control all the factors to make it as identical to nature as possible, then experiment on that.
Once you dump it in nature, there is no setting it right again.
