The power outage was a result of a switch that exploded at the Monacillo Transmission Center. Puerto Rican officials are still investigating the cause, though they told CNN it was due to a mechanical failure. “We started a damage assessment process to see what went wrong,” Justo González Torres, executive director of the power authority, said in a press release. “We understand that it could have been a mechanical failure within the system.”

This incident serves as a reminder of the many challenges the U.S. territory is facing to return power to the U.S. citizens who remain in Puerto Rico after Hurricanes Irma and Maria tore through it last year. It’s been nearly five months since Hurricane Maria destroyed its electric grid—one that was falling apart long before the hurricane threw it off the edge.

The government should have long ago replaced some of the infrastructure needing work now, The Associated Press reports. The island’s fiscal crisis—which has left PREPA in $9 billion of debt—is to blame. Human rights activists and groups have called for the federal government to relieve Puerto Rico of its $74 billion in debt so that the island can properly rebuild in the onslaught of these natural disasters, especially so that municipalities are prepared come this year’s hurricane season. A disaster aid package President Donald Trump signed last week will, however, provide the territory with a much-needed $16 billion in aid.

Still, at least 375,000 PREPA customers remain without power, with the Caguas region in the east suffering the most. Power is supposed to be back by May—just in time for the next hurricane season.