The compound is specific if applied very carefully and conditions stay static. But things sometimes go awry and there are some ancillary negatives. The alternative, in relation to the fishery, is not pretty, could devastate the Lake trout fishery and put another serious dent in the salmon, brown and atlantic populations . I even watched a gull pick one off a steelhead two falls ago in the riff going up out of the staircases.
I did not think they did any of the tributaries every year, but maybe they hit the Salmon harder due to the large numbers of returning fish.
The algae and turbidity have to do with increased use of the watershed surrounding the river: aging of the infrastructure, 55 gallon or older steel tank systems, or systems not maintained (expected life of an onsite wastewater treatment system is 20-25 years), all those Amish horses pooping all over the road, more active dairy, new construction, and just more people disposing of nutrient containing by-products of life in Steelhead Paradise. Pretty soon the camel is carrying a lot of extra straws!
Once the crowds hit town in the fall, you used to be able to see the effluent coming out of the Pulaski Waste Water Treatment Plant sometimes (the discharge is about 3/4 of the way down the Black Hole. I know they did a lot of upgrading, but the population swells considerably in the fall. And NYS is the Greek Yogurt Capital of the World now, all those extra cows gotta go sometime (all the time!) and the manure generally ends up spread on a field some place.