By some estimates, the Great Pacific Garbage Patch consists of more than 80,000 tons of waste and debris, tossed together by the currents into a sort of island of lost toys, minus the island. As it grows, scientists say, so does the danger it poses to the health of the ocean.

The 2,000-foot-long boom, which arrived at the garbage patch after a voyage of about 1,400 miles, was designed to trap the trash so that it could be returned to shore. The Ocean Cleanup’s goals were ambitious: 150,000 pounds of plastic in Year 1, with more booms to follow. Within five years, the group hoped, half the debris would be collected.

But on Monday, the organization said that in a routine inspection over the weekend, it found that an end-section of the boom almost 60 feet long — 18 meters — had detached. The boom will be taken back to shore as soon as weather allows, the group said.

The Ocean Cleanup said it appeared that material fatigue and “local stress concentration” might have caused the fracture in the multimillion-dollar structure.

Skeptics had raised doubts about whether the boom, known as Wilson, would do much good and whether it could hold up to the forces of nature.