But there's hope, according to experts and activists, who say there are a slew of steps you can take to help make a difference.
"Things are bad but we're at a state where we can definitely make a change," said Samantha Mackiewicz, director of World Oceans Day.
World Oceans Day takes place every year on June 8 to celebrate Earth's waters and highlight the challenges they face. This year, the focus is on plastic pollution, which is permeating our oceans.
"What we're asking people to do this year is to eliminate or reduce their use of single-use plastics — so that's bags, bottles, straws — in honor of World Oceans Day," said Mackiewicz.
"The hope is that if someone can take that action for one day, hopefully they could carry that behavior over beyond World Oceans Day and into the rest of the year," she said.
Here's a look at how you can curb your plastic use — and other actions experts suggest — to have a positive impact on our oceans' health as we mark World Oceans Day.
Bring a garment bag to your dry cleaner
"Invest in a zippered fabric bag and request that your cleaned items be returned in it instead of sheathed in plastic," says the Natural Resources Defense Council, a New York City-based non-profit organization.
There are likely dozens of other ways you could cut down on single-use plastics, which are things like Ziploc bags, disposable coffee-cup lids and plastic wrap. Try using your own on-the-go mug when you hit up a coffee shop, carrying a reusable water bottle at all times, including while traveling, and bringing your own utensils to work to avoid relying on plastic cutlery.
Experts and activists also suggest using cloth bags instead of disposable ones for groceries, buying in bulk to cut back on packaging, and boycotting products with microbeads, which are tiny orbs of plastic that can be found in products like facial scrubs and toothpaste. They slip through water treatment plants and can be eaten by marine animals.
All of those small steps could have a cumulative effect of cutting down on the colossal amounts of plastic that are ending up in our oceans. Just days ago, nearly 20 pounds of plastic bags and other plastic trash were pulled from the stomach of a pilot whale that died in Thailand, according to officials.
One study has found that tossed plastic trash could outweigh fish by 2050 if we don't make changes.
Plastic breaks down over time and turns into little pieces that don't go away "but become almost part of the food chain," said Whitley Saumweber, an ocean policy consultant in Washington, D.C.
"These small pieces of plastic are everywhere in the ocean and are being consumed by everything from the smallest plankton all the way up to whales," he said.
Now, talk about it
"Talk to your friends and family about why the ocean is important and why you take steps to help it, and challenge them to do the same," said Mackiewicz, the director of World Oceans Day.
Others suggest carrying that conversation into public places.
"If you're at a restaurant and you ask not to have a plastic straw, then they're going to start thinking, 'Hmm, that's interesting. I wonder why they did that,'" said Kallan Benson, a 14-year-old oceans activist from Maryland who won the National Aquarium's Promise for the Planet award this year.
Benson said the extent to which plastics have permeated our lives and penetrated our environment is "scary."
"As a youth, I know that someday this environment is going to be my responsibility and I'm going to be getting it with all these problems already," she said. "How am I going to clean that up? How are we going to create a livable future for the rest of the generations on this planet?"
An Indian child searches through mud for coins and other items of value along the polluted banks of the River Ganges at Sangam in Allahabad. CREDIT: Sanjay Kanojia/AFP/Getty Images
Plan a cleanup
Mackiewicz said a good way to make a difference is to organize a garbage cleanup now. Whether it's an inland cleanup or one near the coast, plan one in your community, she said.
"No matter how far you live from the ocean, the ocean impacts you," she said. "Everything leads to the ocean, every river. ... So, no matter if you're cleaning inland or on the shore, you're helping the ocean overall."
"Dine discriminately" and "buy American"
One of the biggest issues related to human impact on the oceans is overfishing, said Saumweber. "We've also got a real problem with illegal fishing," he said.
Such practices have left many marine species severely depleted, with some on the brink of extinction, according to the Natural Resources Defense Council (NRDC).
"The simplest thing to do is buy sustainability," said Saumweber.
And that doesn't only apply when at the grocery store. "Dine discriminately," said Sarah Chasis, senior attorney and director of NRDC's Oceans program.
They recommend using the Monterey Bay Aquarium Seafood Watch guide, which provides information to help consumers make choices that have less impact the environment.
Saumweber said a key thing to do when looking to support sustainability "is just buy American."
"We've got the best-managed fisheries in the world here in the States," he said. "By and large, if you're buying an American fish product, you're buying a well-managed fishery."
Another component of this is to fish responsibly, said experts. That includes making sure you know the local rules, having a proper fishing license, and practicing catch and release.
"We are at risk of depleting our ocean fisheries worldwide and so care has to be given in how we use those resources," said Chasis.
Tons of dead fish float on the waters of the Rodrigo de Freitas Lagoon in Rio de Janeiro, Brazil. CREDIT: Christophe Simon/AFP/Getty Images
Ditch your car
Opting for public transportation over driving your car can impact your microclimate, said Lisa Emelia Svensson, director for Ocean at U.N. Environment, the environmental agency of the United Nations.
An action like this can reduce your carbon footprint, and multiplied by the efforts of millions of others around the world, that may help slow global warming and ocean acidification — a change in ocean chemistry which threatens marine life.
Bill Mook, who works in the oyster industry, says he has felt the impacts of acidity firsthand. He said his wake-up call came in 2009 when his oyster farm started having trouble producing oysters.
The challenge was growing oyster larvae, which mature into oysters that we can eventually eat. They are very sensitive to changes in the acidity level of the water.
"We realized that we were having a pH problem, an acidification problem, and started buffering our water, which is the equivalent of putting Tums in the water, essentially," said Mook, who is a Maine-based leader of the Shellfish Growers Climate Coalition and owner of Mook Sea Farm.
"What was surprising was that when we started doing that, it was literally like turning a light switch on and off — or on, I should say. And all of a sudden, each of the larval cohorts returned to their normal biology," he said.
While that basically solved the problem for his oyster farm, the major global challenge of ocean acidification remains.
"In the past 200 years alone, ocean water has become 30 percent more acidic — faster than any known change in ocean chemistry in the last 50 million years," saysthe Smithsonian Institution's Ocean Portal, which is part of its Ocean Initiative.
The oceans soak up about a quarter of the carbon dioxide produced by the burning of fossil fuels, which changes their fundamental chemistry.
Aside from walking, biking or the taking the bus instead of driving, experts and activists say you can also cut your daily emissions by finding ways to conserve energy.
"Energy conservation is a huge, huge benefit to people," said Mook. "And I can show you in my own business how over the years we have adopted technology that has dramatically allowed us to produce more and more oyster seed, for example, in our hatchery with less energy input, and I think that applies to small businesses all over the country, as well as to homes."
Send a message to Congress — or start local
Activists and experts stress the importance of communicating with decision-makers.
Individuals can have an impact on the health of our oceans by supporting policies that reduce carbon emissions, said Saumweber, who served as associate director for ocean and coastal policy in the White House Council on Environmental Quality in the Obama administration. He urged people to work to make sure their elected representatives support keeping high standards for fuel emissions, embrace alternative energy strategies and support subsidies for solar and wind power.
There is also concern about "threatened rollbacks to strong conservation laws that are on the books now," such as the Marine Mammal Protection Act and the Magnuson–Stevens Fishery Conservation and Management Act, said NRDC's Chasis.
The Trump administration has also proposed to open up huge areas of America's coast to offshore oil and gas drilling.
"We all saw what happened with the BP oil spill in the Gulf of Mexico and how damaging that was to coastal communities and fisheries and the health of the Gulf Coast ecosystem," said Chasis.
She urged people to send a message to Congress and the Trump administration through a form on the NRDC's website. "This is a time for people to raise their voices," she said.
Mackiewicz, with World Oceans Day, suggests starting local.
Contacting local leaders "is definitely the first step" in impacting government policy, as well as seeing what you can change in your local communities, she added.
A shovel sits in oil-covered sand at Ao Phrao Beach in Thailand, as volunteers work to clean up the area after a major oil slick hit the island of Ko Samet in July 2013.CREDIT: Nicolas Asfouri/AFP/Getty Images
Experts say recycling is an obvious action to take.
Check on what can be recycled in your community, and make sure you're separating out your plastic — and that it's eligible for recycling, said Chasis.
"I know it sounds a little trite, like 'reduce, reuse, recycle,' but it's really true, and it's something we've gotta change and we've gotta embrace," said Saumweber.
While the U.S. is not the biggest driver of plastic pollution — China tops that list — "it doesn't mean we can't lead by example and it's not important for us as some of the world's major consumers to make sure that we're having an impact on the world through our actions," he said.
Here, a woman collects a sample of the red polluted water flowing from a sewer into the Jian River in Luoyang, north China's Henan Province. The river developed this apocalyptic look after two illegal dye workshops dumped red dye into the city's storm water pipe network.CREDIT: STR/AFP/Getty Images
"Think about it more"
That's what Kallan Benson, the 14-year-old oceans activist, would say to someone who asks what single action they could take to make a difference. The idea is that the more someone thinks about plastics and plastics pollution, the environment and the consequences of our actions, the more likely they are to act on it.
"When we go to the grocery story, we're more likely to bring our own bags instead of getting plastics bags. We're more likely to go out and talk to our legislators about the Styrofoam ban just because we're constantly thinking about it," she said.
"Being more aware is the biggest thing you can do," she added.
More about: pollution