It had been a good morning sea trout fishing. Charter Capt. Harry Demosthenes had piloted the Drum Runner customers spot to spot making catches on the North Edisto River. Then he spotted the hulk up on the bank.

“Wow,” he said “That’s a big dead sea turtle.”

The leatherback turned out to be huge, more than 900 pounds. A tag on her flipper indicated she had come all the way from Trinidad. A boat propeller had gauged her leathery shell and struck her head, but she wasn’t otherwise healthy. A blob of plastic blocked her intestines.

Nearly 1 billion tons of plastic are manufactured around the world each year. Virtually indestructible, they get discarded as litter or wash into waterways often enough that a recent Citadel study estimated more than 7 tons are breaking down to squiggles called microplastics in the tide and waves of Charleston Harbor at any given time.

That kills marine life. In the water, the plastics resemble jellyfish and then smaller organisms that fish feed on. The larger pieces cut off digestion; the microplastics are toxic. No one knows yet what the impacts will be on the food chain and human life.

Sea creatures aren’t the only wildlife at risk. A stork in Europe was found with its upper body stuck inside a plastic bag, according to Defenders of Wildlife. Pelicans, herons, gulls, ducks, opossums and even a boa constrictor have been found snarled in the shreds of plastic bags or six-pack rings. A black bear in the Ocala National Forest in Florida got its head trapped in a plastic jar while rooting through the trash.

The plastics in the leatherback that Demosthenes came across in April 2014 wasn’t a freak of chance. At least seven sea turtles admitted to the treatment facility at the South Carolina Aquarium have had a plastic bag or the remnants of one in their system, said spokeswoman Kate Dittloff.

A green turtle released Friday after treatment and a loggerhead currently in treatment both had plastics in their system. A loggerhead admitted in 2015 began passing pieces of plastic bags and balloons.

A pygmy sperm whale that was found dead in North Inlet in 2010 had swallowed garbage bags and Mylar balloons, said Wayne McFee, National Ocean Service marine mammal stranding program scientist.

“It’s not rare. It’s not really common. But we do see it,” he said.

A more troubling prospect is that toxics in micro-plastics consumed by sea mammals have been shown to cause reproductive problems, he said. The service is launching a study on that.

In the past 50 years, plastics production has grown 20 times to reach that 1 billion tons per year mark, according to Jan Zalasiewicz, Leicester University palaeobiology professor, in a World Economic Report issued earlier this year. Only about 14 percent is recycled.

In the ocean, the remnants of discarded plastic bags, water bottles and bottle caps, fishing line, straws, balloons, beer cups, toothbrushes and other trash break down to microplastics. In spots, as many as a half-million pieces float per every square kilometer, about one-third of a square mile, researchers estimate.

Microplastics are now found in virtually every environment, from the massive ocean eddies to the human body. The Citadel physiology professor John Weinstein, who leads the ongoing plastics study, called the pollution one of the critical environmental concerns facing wildlife today.

“What a shame,” McFee said about the pygmy sperm whale, “these otherwise seemingly healthy individuals.”

Reach Bo Petersen at 843-937-5744, @bopete on twitter or Bo Petersen Reporting on Facebook.