If river water is contaminated with E. coli (probably cows in the river and a feed lot close enough to river for the runoff to reach it ) and that water is used to water your garden how much risk is there. Also I use a sprinkler that is pretty misty , vapors in the air. Can myself or animals be infected by breathing in contaminated mist.
I live down stream of Zion national park ( E. coli levels measured last time was 10 times the safe level ) , grazing cattle in the river and a feedlot very close to virgin river.
Maybe less than 1000 ft.
I have had two bouts with coli and a friend just got out of the hospital from coli.