Wildfires had burned through 11,500 acres east of Card Sound Road as of early Monday afternoon. Firefighters are working to prevent the blaze from threatening U.S. 1.

A wildfire near Florida City that caused Card Sound Road to be closed to traffic in both directions Monday was moving with easterly winds toward U.S. 1, concerning officials who say the highway could have to close if the blaze gets too close.

The two are the only roads connecting the Florida Keys to the mainland.

Wildfire mitigation specialist Scott Peterich said the fire started on April 30 and had burned 11,500 acres as of Monday afternoon. He reported that it was 55% contained.

The fire started in a remote area near the Homestead-Miami Speedway and was being pushed by winds toward Card Sound Road. Peterich said that his agency, the Florida Forest Service’s Everglades Division, was performing controlled burns by Card Sound Road to try to take away fuel from the fire and prevent it from jumping the road and heading toward U.S. 1.

In the event that the main highway does close, Peterich hoped that smoke will have died down enough that Card Sound Road could be reopened, so as not to cut off access to the Keys. Peterich said that scenario has occurred before. The fire could continue to burn for a few more days, he said Monday.

Peterich said that it was difficult to say what caused the fire exactly, but that it involved humans, as there was no lightning in the area recently. As of Monday, he could not say whether it had been set intentionally but was leaning toward the theory that it had been set by an engine spark from a recreational vehicle.

“It’s so hard to find the actual cause when you’re so far out in this remote area,” Peterich said.

The remoteness of the area means that the fire is not currently threatening any structures but has also made it difficult for firefighters to bring equipment out into the wetlands.

Firefighters have been using Type 6 engines, smaller engines that look like a pickup truck with a large water tank on the back, to fight the fire. Those tanks carry about 300 gallons of water each.

Peterich said the fire is “meandering” and leaving small pockets of unburned fuel around the area. The main goal is to keep it on the eastern side of Card Sound Road and prevent any further road closures.