Turns out, like so many other things in life, that's not a True/False question. There is a serious lack of data in most areas, people really haven't been watching the oceans very carefully or for very long. But based on the data that do exist, human impact has been named as a large factor in many hypoxic regions around the world -- and there seem to be clear indications that they're getting worse and more numerous.
Scientists have been circumspect in their assessment of the dead zone off Oregon -- the immediate oceanographic factors identified are natural. But the jury is still out on the bigger picture -- how unusual is this? why is it unusual? And since it's tied to weather patterns, human impact is implicated, but weather analyses are so complex that they defy a single person's ability to comprehend.
But befuddlement is natural too, no? As is irresponsibility?