@dcowell65 - you are right that barnacles and other salt water critters won’t survive in fresh water, so won’t become invasive. But barnacles and things attached to the boats don’t seem to be considered the problem. Instead, it is ballast water. See https://en.wikipedia.org/wiki/Dispersal_of_invasive_species_by_ballast_water for info.
The zebra mussel, one of the invasives that is currently checked for at OR check stations, has been primarily spread by ballast water.
From my experience, the Columbia is fresh water from about 10 miles upstream from the mouth on up. So Longview, Portland, etc. are all fresh water ports.
Ships fill their ballast when they load, to balance the boat. So the worry would be ships going from one fresh water port to another, and carrying invasives from one port to another. There actually are a lot of fresh water ports. Top of my head just in the US, and likely not a complete list, are Stockton, Benicia, Rodeo, and Sacramento in California, pretty much the whole Missippippi River, don’t recall many large ships going upriver on the Hudson, but that would be; all of the Great Lakes; etc.
There are some rules put in place to try to keep ballast water from spreading invasives. Some details/links at: https://en.wikipedia.org/wiki/Ballast_water_discharge_and_the_environment#United_States