The outage undermines already slow repair work after Hurricane Maria hit the island.

Millions of Puerto Ricans are again without power after a high-voltage transmission line that had been repaired by Whitefish Energy, a Montana contractor now facing an FBI investigation, failed.

The Puerto Rico Electric Power Authority reported that power generation across the island plummeted from 40 percent to 18 percent on Thursday, a major blow to the island’s grueling recovery after Hurricane Maria struck 50 days ago.

Blackout Puerto Rico
PREPA confirms power generation has plummeted to 18% after a failure of Cambalache Manatee 230KV line. Municipalities in the North have been affected.
It could be tonight or tomorrow morning before power is restored.

— David Begnaud (@DavidBegnaud) November 9, 2017

That means that the vast majority of the island’s 3.4 million residents are again without power, extending what was already the longest power outage in US history. The blackout struck the northern part of the island, including parts of the capital, San Juan.

The lights just went out at the Puerto Rico federal emergency command center.

— Frances Robles (@FrancesRobles) November 9, 2017

Without electricity, many health and sanitation systems will go offline or go back to relying on diesel-powered generators.

As Vox has reported, Puerto Rico’s electric grid was vulnerable and dilapidated before the storm due to PREPA’s long history of financial woes and minimal maintenance and investment. But since the storm, the rebuilding of the grid has been further compromised by questionable decisions.

The largest repair contract, valued at $300 million, was awarded to Whitefish, then a two-person company, rather than invoking mutual aid agreements with other utilities as power companies in Florida and Texas did after Hurricanes Irma and Harvey.