Photo: Amy Collenberg.

UPDATE, 6:16 p.m.: Rescuers have determined that the vehicle is unoccupied. They’re going to be looking around in the area just to make sure that no one was ejected from the vehicle and injured as it went into the river. Otherwise, they’ll tow in out and haul it away.

The Coast Guard, Calfire, Arcata Fire, Humboldt Bay Fire and the California Highway Patrol have all been at the scene at one point or another. Numerous surrounding fire departments are providing fire service coverage while engines attend to this incident.

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UPDATE, 6:05 p.m.: Just to be clear: Emergency personnel on scene do not yet know if anyone is in the vehicle. The rescue swimmers are needed to ascertain whether or not anyone is in the vehicle.

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UPDATE, 6 p.m.: A Coast Guard helo passing overhead is trying to get a rescue swimmer lowered down to the scene.

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UPDATE, 5:46 p.m.: Rescue units were briefly canceled on report that the incident was “not as reported,” but the stand-down order was quickly reversed. A full rescue operation is underway.

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A car is in the water at the public boat ramp at Mad River Beach. As noted below, a vehicle was spotted in the river, on its hood with only tires visible, at 5:30 p.m.

According to scanner traffic, rescue swimmers are being summoned to the scene.

Follow updates from the CHP below.