Which sentence doesn’t belong?

A. Horseshoe crabs crawl on colonies of coral.

B. Blackfish and angelfish swim in the green-tinted water.

C. Candy wrappers and plastic bottles drift with the tide.

Did you pick “C”?

If so, bingo!

Garbage does not belong in the ocean. And divers from New York have decided to do something about their city’s underwater trash.

The divers arrive on a thin strip of sand at the farthest, watery edge of New York City. Air tanks are strapped to their backs. They wade into the Atlantic Ocean.

Suddenly, no concrete. No traffic. They’re in a whole new underwater world. One thing it has in common with dry land? Trash.

“Every month we have a prize for the weirdest find,” says Nicole Zelek. She started a dive school called SuperDive. Four years ago, her school launched monthly cleanups in Far Rockaway, New York. What do divers find? Clumps and clumps of fishing line. Goat skulls. Once they found a whole ATM machine! (There was no money inside. Drat!)

“Tons of crabs and horseshoe crabs—which are under threat—get tangled in the fishing line, and then they die,” Ms. Zelek says.

The best way to combat plastics going into the oceans? Use less plastic and recycle or dispose of it properly. The cheapest way to clean up the damage already done? One volunteer at a time.

Surface trash might be easy enough to clear with a rake. But the task gets more challenging beneath the water. Layers of fishing line have accumulated over many years. And until a few years ago, no one was scooping out the line, hooks, and lead weights fishermen left behind.

Untangled, a pound of medium-weight fishing filament would stretch to a bit more than four miles. How many miles of it remain in the sea? That’s anybody’s guess.