Updated at 1:41 p.m.

ALAMO — Burning embers that “jumped” the river may have caused a fire that has grown to affect more than 320 acres at the Santa Ana National Wildlife Refuge, an official with the park said Thursday.

The number of acres affected dropped to 285 acres as of 1:41 p.m. Thursday.

Robert Jess, Lower Rio Grande Valley National Refuge complex project leader, said it’s likely a controlled river cane burn on the Mexican side spread north with high winds.

At about 3 p.m. Wednesday, wildlife fire crews were called to the refuge after officials reported a fire that began along the river bank, Jess said.

Further exacerbating the fire are dry remnants of a nearly 10-year-old flood that covers the grounds at Santa Ana, called the duff, or the dried remains of dead trees and other vegetation, further fueling the fire to burn overnight, according to Jess.

He said fire crews from Alamo, Donna, San Juan, Pharr, and U.S. Fish and Wildlife are being cautious in their approach to the fire — citing heavy brush as a factor in their limited access to fight the fire directly.

Anywhere from 15 to 25 crew members worked the fire overnight, the complex project leader said. Jess said fast-moving winds are expected to whip fires and could continue to cause issues for the crews.

Crews are utilizing the existing trails and roadways to create the containment line ceding the 285 acres of thick vegetation.

“It’s a line we drew in the sand,” Jess said. “This is the point where we’re not going to allow it to get past this.”

Jess expects crews to work the fire for at least a few more days before determining when it would be safe to open the refuge to the public.

Rey Navarro, assistant fire management officer with U.S. Fish and Wildlife, said they expect crews to have the fire 75 percent contained by this afternoon.

Check back for updates.