The collapse of a giant wind turbine blade off the Massachusetts coast confirmed Peter Kaizer’s worst fears about the dangers a new clean energy business could pose to fishermen like him.

Jagged pieces of fiberglass and other materials from the shattered blade drifted with the tide, forcing officials to close beaches on Nantucket and leaving Mr. Kaizer worried about the threat the fragments might pose to his vessel and other fishing boats, especially at night when the debris would be harder to avoid.

“All these small boats could be subject to damage,” Mr. Kaizer said. “Everyone wants this green legacy, but at the cost of what?”

The blade, which was more than 300 feet long, failed in July, but the repercussions are still unfolding at the $4 billion project that it came from — Vineyard Wind 1. Developers had hoped to finish the project this summer, making it the first large-scale wind farm completed in U.S. waters, but now that goal will take a lot longer than expected.

The blade failure is the latest problem slowing the fledgling U.S. offshore wind industry, which the Biden administration and East Coast states are counting on to deliver emission-free energy to millions of people from Virginia to Maine. President Biden and governors of those states had hoped to follow the examples of European countries like Britain and Denmark, which have plunked down thousands of wind turbines around the North Sea.

But the American offshore wind business has struggled to get going because of cost overruns, delays in issuing permits, and opposition from local residents and fishing groups. Several large projects were canceled or postponed even before the blade failure in Massachusetts because their costs increased sharply and developers did not anticipate supply chain problems and higher interest rates.