Todd,

It's difficult, but possible to do on at least some streams. Timing and amount and type of fertilizer are critical. As water flows downstream, the fertilizer is "processed" and taken up by whatever can use the nutrient enhancement. As long as this happens before the next organic inputs from farms or factories or peeing fishermen, there should be no problem. But if there is a screw-up, then there would be a risk of creating a biological oxygen demand (BOD) or chemical oxygen demand (COD), and then fish in that area ain't gonna' be happy.

So, short answer is yes. But with a lot of care.

Sincerely,

Salmo g.