Farmers have been polluting forever - those nitrates and slurry spreading derogations; the poisons they use for raptors, for badgers, for foxes etc; the pesticides and insecticides on crops, some of which are used to just ripen cereal crops for harvesting; monocultures, drainage, and worst of all the inhumane and cruelly polluting and disgusting factory farms for cows, beef, pigs and chickens. They also use lots of medications, antimicrobials and antibiotics to keep the animals ‘healthy’ until slaughter.
Opposing any intensive agriculture operation rarely results in a win, until it’s years down the line and everyone can see the opponents were correct all along - think of the River Wye as just one example.