WAIPAHU — The Pouhala Marsh Wildlife Sanctuary is only about a mile from their campus, but at least some of the roughly 120 Waipahu High School sophomores who visited the 72-acre preserve yesterday and Tuesday did not even know of its existence, much less visited there.

They know now.

"I thought this place would be more of a barren wasteland with very little growing here," said Royce Abcede, 14. "But there's a lot growing here."

The students were taking part in the third annual Wetland Field Day. Experts located at four different stations gave the students instruction in water sampling, native plant identification, native bird identification and soil education.

The whole idea is to get the students aware and, hopefully, interested in the environment around them, said field day coordinator Iwalani Sato, the city's storm water public education and outreach coordinator.

Deli Oania, a 10th-grade language arts teacher, said the program works. Large-scale marsh cleanups are typically held on a Saturday in the month after the field days and students are asked to volunteer.

"Last year, I was expecting maybe 20 students and 54 of them showed up," Oania said, explaining that she ran out of T-shirts to distribute. "And it was 8 o'clock on a Saturday. Who in their right mind wakes up early on a Saturday?"

Randall Wakumoto, a civil engineer with the city's Department of Environmental Services, showed the students how to measure the temperature, pH, ammonia, nitrate and phosphate levels of the water in Kapakahi Stream. Wakumoto reminded the students of what happened at Wahiawa's Lake Wilson several years ago when there was an explosion of the weed Salvinia molesta that smothered the waterway.

"The reason for that was there was a lot of nutrients in the water," Wakumoto said. "And the fish can't live in that water."

At another station, biologist Gregory Koob of the U.S. Natural Resources Conservation Service explained how Pouhala was once the site of many Hawaiian fishponds but then was allowed to become a dump. Now it's being restored as a sanctuary for the ae'o, or Hawaiian stilt, an endangered species.

The tall, slender bird with pinkish-red, stick-like legs is white on its face, neck and stomach, with black on its head and its bill.

"The stilt likes shallow water for feeding and nesting purposes," Koob said, pointing to a dried-out mud flat that had been dug up by volunteers from what was once the heart of an illegal garbage dump.

Pouhala is the largest remaining intact wetland habitat in Pearl Harbor, making it a key resource for those seeking to repopulate the ae'o. Ducks Unlimited, the state Department of Land and Natural Resources, U.S. Fish and Wildlife, the city Department of Environmental Services and several other agencies have taken the lead in preserving the habitat. The Hawaii Nature Center, meanwhile, organizes a monthly restoration work day and also takes school groups onto the site.

Usually filled with water, the bed was dry yesterday and covered by a layer of dirt with exposed salt and the bones of fish. "It's just like Jurassic Park!" exclaimed one student excited to see the skeletons of fish.

"Eventually, this whole area will be cleared and ponds will be created," Koob said.

Tenth-grader Melvin Pua, 15, said he remembers visiting Pouhala five years ago and how it was overgrown with mangrove and other non-native vegetation. "This is much different than the last time," he said. "There used to be trash over there."

Said Waipahu biology teacher Sherry Tenn: "Our goal for this project is to get them to appreciate their environment, to be respectful of their environment and to take care of it."

That sentiment was echoed by Rick Barboza, owner of the Hui Ku Maoli Ola native plant nursery in Kane'ohe who volunteered yesterday to teach the students how to identify the native and non-native plants around them.

"This gives them a better idea of what their surroundings are," Barboza said. "They've got a treasure here and we're trying to get them motivated to learn about it, recognize that this place is special."

"I didn't know it was a dump and that there used to be ponds over here in its natural state," said sophomore Mena Fiaavae, 15. Fiaavae said one lesson she'll take away is how to identify non-native plants that are bad for the environment.

Once she spots them now, she said, she'll be able to uproot them.

Reach Gordon Y.K. Pang at gpang@honoluluadvertiser.com.