You’ve signed up to save the whales and buy dolphin-free canned tuna. But rescuing the entire ocean? That may be just a bit too titanic. From endangered sea turtles to escalating pollution, the issues are as varied as they are colossal. Having trouble wading through them all? Here are three top concerns—and what you can do.

1. Dead zones

The seafloor encompasses vast networks of life (think crabs, shrimp, clams) that support the ocean’s food chain. However, large swathes of these species’ habitats—particularly along coastlines and at river mouths worldwide—are dying off as bottom water becomes increasingly oxygen deprived, a result of excess fertilizer runoff. The most notable dead zone lies in the Gulf of Mexico; it’s more than 8,000 square miles.

What you can do:Always choose organic when buying fertilizer-intensive products such as corn, soy, or cotton. More info: oceanconservancy.org and oceanchampions.org.

By the numbers

  • 5: Percent of humans’ dietary protein that comes from the sea
  • 50: Percent of Earth’s species that live in oceans
  • 71: Percent of the planet’s surface covered by ocean
  • 97: Percent of the planet’s water that is ocean
  • 95: Percent of ocean that remains unexplored
  • SourceL NOAA.gov.

2. Contamination

Hidden dangers to fish lurk in many personal care products, perfumes, and detergents, including those containing triclosan and phthalates; synthetic musks such as galaxolide and tonalide; or bisphenol-A (BPA) leached from plastic containers. Expired prescription or over-the-counter medications that get flushed down the drain also contribute to ocean contamination. Scientists don’t yet know all the impacts, but evidence points to these chemicals causing behavior changes that affect fish species’ survival.

What you can do:Purchase natural beauty products free of toxic nasties. And don’t flush meds! Contact your pharmacy or health care agency to ask whether they accept unused or expired prescriptions for disposal or redistribution. More info: theoceanproject.org.

3. Depletion

More than 70 percent of marine stocks are exploited or depleted, according to the U.N. Food and Agricultural Organization. And even though fishing methods are getting more efficient, the Ocean Conservancy notes for every 4 pounds of fish caught, 1 pound of “other animals,” or bycatch, is thrown away—that includes turtles, sharks, and whales. Conventional fish farming may not be the answer; this method’s byproduct pollution, parasites, and disease can leach into the ocean, threatening wild fish populations.

What you can do: Eat low on the food chain—abundant species, such as sardines and squid, reproduce quickly. And ask your market and restaurants to stock and serve fish exclusively from eco-conscious farms and fisheries. More info: seafoodwatch.com and seafoodchoices.com.