With wildfires raging across 40,000 acres of Everglades National Park, the federal government opened a flood gate on the park's northern boundary yesterday to let water flow into parched marshes and help keep the blaze away from important wildlife habitat and cultural resources.

The measure may be insufficient to prevent the destruction of critical habitat for the endangered Cape Sable seaside sparrow, a species that exists only in the Everglades. The Army Corps of Engineers said the increased flows through the Shark River Slough should help protect some of the bird's nesting areas.

The fire began Wednesday near the park's Chekika Visitor Center, and investigators believe it may have been started by humans, although not necessarily intentionally.

A second major fire covering about 25,000 acres of exposed grass and muck on Lake Okeechobee's bottom far north of the park also remained a concern for firefighters, although winds were pushing the flames toward the lake's interior and away from homes and businesses.

The park fire was about 30 percent contained as of this morning, officials said, with rising humidity and scattered rain showers expected to provide relief.

So far, the fire has not threatened any residences, and winds this week were driving the fire away from Miami-Dade County suburbs. But smoke continues to hover, causing respiratory distress.

Two prisons near the park, including the 1,700-inmate Everglades Correctional Institution, were evacuated due to fire and smoke concerns. Meanwhile, as a precaution, firefighters began cutting swaths of melaleuca forests, which act as fuel for the wildfires, near more populated areas of southwest Miami-Dade County.

Yesterday's emergency water release by the corps and the South Florida Water Management District increased flows through a flood gate along U.S. 41, also known as the Tamiami Trail.

Dan Kimball, the Everglades park superintendent, said in a statement that the additional releases will increase water flows by only "a very small amount," but the measure "will keep the slough from drying out as quickly in the coming days."

Water flows through the Shark River Slough are expected to increase slowly over the next several days, and Kimball said he is confident the measure will diminish the fire's intensity and protect resources.