dense fog
thick fog
heavy fog

But no one could see them in dense fog like this.

At the time there was dense fog in the area.

The day began with a dense fog over this beautiful but difficult course.

There was dense fog, however, and nothing could be seen.

The field was covered by a dense fog on the morning of 14 March.

But such questions hang in the air like a dense fog.

But more recently, a dense fog has formed around the company.

He emerged from it as if coming through a dense fog.

The accident happened at 8:55 in dense fog on a Sunday morning.

It was like looking out of an airplane window into dense fog.