Mr. Ingólfsson’s trawlers can now move in and out only at high tide, and his business suffers for that. Last winter, two were stuck outside the harbor when a storm hit, he said, forcing the catch to be offloaded at another factory on the east coast, leaving scores of workers at his Höfn plant idle.

“Unless we find a solution,” he said, “things will just get worse.”

Glacial melting is also expected to oversaturate watersheds in the next century, and scientists predict that they then will dry up, forcing energy producers to adapt. Landsvirkjun, the state-run energy company, which generates three-quarters of Iceland’s power, is building room for additional water turbines at its dams. It is also building new capacity for wind turbines to operate when the glaciers die.

“From a design perspective, we’re taking into account what will happen in the next 50 to 100 years,” said Óli Grétar Blondal Sveinsson, the executive vice president for research and development. “There will be no glaciers,” he said flatly.

That prospect has jolted Icelanders — and some visitors — to a realization that they are witnessing a treasure vanish. Steinthór Arnarson, 36, quit his job as a lawyer three years ago to open a tour business at the Fjallsárlón lagoon, employing 20. He takes visitors on inflatable boats around iceberg-studded waters that barely existed two decades ago.