The Northwestern Hawaiian Islands are remote, with just 10 tiny atolls spread across 1,200 miles of Earth's largest ocean. They have a few seasonal residents but no permanent human population, instead providing an expansive habitat for coral, fish, seabirds, marine mammals and other wildlife.

Yet despite their distance from civilization — and their inclusion in a 140,000 square-mile marine preserve — these otherwise pristine islands are littered with garbage. During a recent cleanup mission, 17 divers from the U.S. National Oceanic and Atmospheric Administration (NOAA) collected 57 tons of trash in 33 days, ranging from bottle caps and cigarette lighters to long-forgotten fishing nets.

That's 114,000 pounds, or a daily average of 203 pounds per diver. Although heavy machinery helps with some heavy lifting, the fragility of coral reefs requires divers to do most of the work by hand.

"The amount of marine debris we find in this remote, untouched place is shocking," says Mark Manuel, operations manager for NOAA's Coral Reef Ecosystem Division, in a statement about the cleanup.

How did so much trash get there? The islands are in the Great Pacific Garbage Patch, one of several places on Earth where ocean gyres hoard plastic that drifts from rivers, shores, ships and other sources. Much of this slowly becomes insidious microplastics, but it can also pose a more immediate threat, like plastic shards eaten by birds or fishing nets that can entangle whales, dolphins, seals and turtles.

NOAA's divers saw the latter firsthand during their cleanup, rescuing three endangered green sea turtles that were wrapped up in derelict fishing gear. "We probably got to them just in time," Manuel tells Hawaii News Now. "Who knows how long they would have stayed alive if we didn't get to them."

green sea turtle in fishing net

A green sea turtle struggles in a net at Pearl and Hermes Atoll, one of three turtles rescued during NOAA's 2014 cleanup. (Photo: NOAA)

Yearly cleanups have been held in these islands since 1996, totaling 904 tons of trash over 19 years — placing this year's 57 tons about 9 tons above average. "This mission is critical to keeping marine debris from building up in the monument," says Kyle Koyanagi, Pacific Islands coordinator for NOAA's Marine Debris Program. "Hopefully we can find ways to prevent nets from entering this special place, but until then, removing them is the only way to keep them from harming this fragile ecosystem."

While fishing nets are often the main threat for coral reefs and large marine animals, small plastic waste is also a big problem both in the water and onshore. The divers thus combed beaches as well as the seabed, finding more than 6 tons of plastic on the shores of Midway Atoll alone. That included 7,436 hard plastic fragments, 3,758 bottle caps, 1,469 plastic beverage bottles and 477 lighters. Many of these inedible items pose a mortal danger to seabirds, which often unwittingly feed them to their chicks.

Hawaii marine debris

NOAA divers confront a bus-sized mass of fishing nets that was reported last September at Pearl and Hermes Atoll. (Photo: NOAA)

The dive team also recovered two 30-foot boats, presumably lost from Japan during the 2011 tsunami, and spotted two others they weren't able to remove. NOAA scientists will inspect all the wreckage and check with Japanese officials to determine its origin, the agency says in a press release.

The 2014 expedition filled every garbage container onboard the NOAA ship Oscar Elton Sette, forcing divers to begin dumping recovered nets and other debris onto the vessel's decks. "There's a point when you can handle no more," Manuel says, "but there's still a lot out there."

All fishing nets found during the mission will be used as fuel to produce electricity in Hawaii, part of the state's Nets to Energy program, to which NOAA has donated wayward fishing gear since 2002. Every 100 tons of nets recovered can generate enough electricity to power 43 homes for a year.

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.