More likely there will be a big algae bloom in the river and down the coast, with accelerated growth of kelp. Could be a good thing eventually. We really don't understand nitrate in the marine environment very well.
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.