I was just revising the “marine chapter” for a textbook I have coauthored, and looking at reviews from professors who had taught a conservation course using our first edition. We were criticized for making marine conservation too much about fishing and marine protected areas, while neglecting ocean pollution as a big deal, and probably the greatest threat to our oceans.

It turns out these critics were right.

For much of human history the ocean has been viewed as a place to dispose of waste where it would be so diluted that it does no harm. We now know better.

Dead zones, floating mats of plastics, and toxic chemical residues in marine fish tissue are striking evidence that human waste and by-products could be every bit as much of a threat to our oceans as over-fishing.

Dead zones now affect more than 400 systems, and cover vast areas of the ocean — more than 475,000 square kilometers. Plastic debris in the oceans is now so common it is hard to find a beach without washed up plastics. This plastic is much more than a matter of aesthetics; all sea turtles, 45% of marine mammals, and 21% of seabird species are harmed by plastic.

The sheer volume of human waste products and the fact that most people live along coasts means that there will be no simple, single measure that can address marine pollution.

Take something as specific as cigarette butts — over 4.5 trillion cigarette butts are discarded annually, and researchers have observed a 96-hour mortality effect (measured as LC-50) in larval topsmelt (a Pacific ocean silverside) at a dilution of one cigarette butt per liter of water. Latte-drinking enthusiasts in my hometown of Seattle have given rise to elevated caffeine concentrations in Puget Sound, which are known to cause chemical stress in mussels and other marine invertebrates.

So what are we to do?