Los Angeles County sheriff’s and fire department divers are searching Pyramid Lake after a 23-year-old man failed to resurface after swimming Monday morning.

The possible drowning was reported about 10:50 a.m. at 43100 North Pyramid Lake, according to the Fire Department.

The missing Los Angeles man was on a pontoon boat with three friends when he went swimming without a life vest, according to one of the other men on the pontoon.

By 12:20 p.m., the Fire Department began releasing some resources from the scene, Inspector Sean Ferguson told KTLA.

The search area is hard to access and officials are relying on the dive teams amid the ongoing search effort, Ferguson said.

Rescuers expect to remain at the scene into the evening.

No further details about the incident have been released.

Editor’s note: A previous version of this story gave the incorrect name of the lake and incorrectly stated that the missing man fell off the boat. The post has been updated.