It’s a long ways from Corvallis to the Pacific. 100 miles down river to Portland and the Columbia River, then 100 miles from Portland to the sea. All in rivers that may be approaching flood stage after weeks of heavy rain.
Even so, given that the nitrate would be in solution as opposed to a sediment, the bulk of that nitrate goes to the ocean. I didn't say there would not be an effect downstream; I implied that it is neglectful not to mention what it does in the coastal marine environment, which would be bigger in total magnitude and isn't all bad.