LESBOS, Greece — A young woman from Norway stands on the beach of this island in the Aegean Sea, scanning the horizon through binoculars for rubber dinghies carrying refugees and migrants. The telltale sign is a flash of orange, the color of life jackets.

She spots one and calls to her fellow volunteers for help. Their group of about 20, named A Drop in the Ocean, gathers around her. They wave flags and and yell at the boat to come their way.

“Hello! Welcome to Europe!” they shout. Several wade waist-deep into the water and pull the boat to shore, then help some 40 Afghans, including at least 15 children, on to dry land.

This scene plays out all day, every day on Lesbos, the epicenter of a migration crisis that is only increasing in scale. Approximately 125,000 refugees arrived in Lesbos from Turkey in October, double the number in August, according to the International Rescue Committee (IRC). They are escaping wars and violence in Syria, Afghanistan, Iraq, Eritrea and elsewhere. More than 791,000 have arrived by sea since January.

What sets this humanitarian crisis apart is the centrality of volunteers. On Lesbos alone, they number well into the hundreds. They are lifeguards from Spain, doctors from Holland, trauma counselors from the West Bank, nurses from Australia, a cook from Malaysia, and all manner of ordinary people pitching in however they can. Many come on their own dime, taking time off from work or pausing their lives indefinitely. They fill in critical gaps created by a perfect storm of political weakness and limits to aid: a Greek government in severe economic distress and without capacity to take control; a European Union strangled by politics as it struggles to define a uniform migration policy; and international aid groups that have been slow to move in because they do not normally operate in industrialized nations — and have to start their operations from scratch in a place like Lesbos.

Meanwhile, the boats keep coming, and grassroots volunteer efforts have grown increasingly sophisticated. A group called O Allos Anthropos, Greek for “The Other Person,” cooks and hands out free meals for thousands of refugees daily. A Drop in the Ocean runs its own camp for just-arrived refugees, particularly families with small children, where it provides food, tents and donated clothing. Yet another group, the Starfish Foundation, set up a central bus station for refugees in the parking lot of Oxy, a cliffside nightclub with stunning sea views. Volunteers there give out handmade bus tickets to the two official camps in the island’s south.

But as winter sets in and the sea crossing grows more dangerous, the lack of an officially coordinated emergency response could lead to higher death tolls. Though volunteers have tried organizing themselves in recent months — they now hold weekly meetings with aid workers from international organizations such as the IRC, United Nations High Commissioner for Refugees (UNHCR), and Doctors Without Borders (MSF) — most are not trained in crisis management. They vastly outnumber aid workers on the island, but for many, it’s their first experience with a humanitarian disaster. And because they’re in Greece temporarily, on hiatus from paid jobs back home, the high turnover means many must leave the island just as they are beginning to understand their roles.

On Oct. 28, that volunteer-led crisis response system was tested when five separate shipwrecks occurred within a few miles of the island. One was a wooden boat carrying some 300 people. The Greek Coast Guard, in coordination with the Spanish lifeguards and local fishermen, rescued 242. Volunteer paramedics and doctors waited onshore, then performed CPR and emergency first aid on victims as they came off the Coast Guard vessels. Bodies have been washing ashore daily since then.

Many volunteers feel the major international aid groups have left them to handle the crisis alone. No one is truly in charge; volunteers carve out responsibilities for themselves and try to coordinate among themselves. The UNHCR, typically charged with coordinating responses to disasters of this scale, has borne the brunt of their criticism. But it only steps in at the invitation and direction of national governments. And the Greek government, mired in bureaucracy, has been slow to cede control to the agency.

“In other parts of the world, we have normal operations and the UNHCR has a lot of authority,” said Ron Redmond, a spokesman for the UNHCR office in Athens. “Here, the government runs the show and we do what they ask us.”

Until this summer, the UNHCR’s office in Athens only had about 10 employees; “guys in suits,” Redmond said, not field officers who are actually on the ground arranging for supplies and ensuring the most vulnerable refugees get special protection. The UNHCR now employs about 120 in Greece, including more than 20 on Lesbos, with many called in from postings in Jordan, Iraq and Afghanistan.

The Greek government, still struggling with the latest chapter of its financial crisis, has spent $1.65 billion on the migration crisis over the past 18 months, according to the office of Greek migration minister Yiannis Mouzalas. Meanwhile, the European Commission has so far released only about 42 million euros of the 259 million euros it has allotted Greece to help deal with the flood of migrants.

But it’s unclear just where all that money has gone. On Lesbos, it is volunteers who are crowdfunding for basic supplies and organizing storehouses of donated items. Even seasoned aid workers and volunteers have said the official Greek response to the migrant crisis is shockingly ineffective.

“In other countries, you expect these things,” said Julia Gozalbes, who volunteers with Doctors Without Borders on Lesbos and has previously served in South Sudan, Haiti and Pakistan. “But this is Europe. We have the resources, we just need to get them here.”