ABANDONED AS a city water source over 50 years ago, East Park Reservoir reverted to nature and became a pristine lake, home to hundreds of native and migratory bird species but fenced off from its Strawberry Mansion neighborhood.

That will change today when North Philly's hidden Fairmount Park oasis is reborn as "The Discovery Center" - a 50-acre, Outward Bound/National Audubon Society lake-and-woodlands paradise where, beginning next summer, thousands of Philly kids can feel their spirits soar on the high ropes course.

By the summer of 2017, when The Discovery Center is built, kids can canoe on rechristened Strawberry Mansion Lake, hike around the 37-acre former reservoir and peer through binoculars to come face-to-beak with thousands of woodland and water birds.

"The power of this experience is the discovery," said Katie Newsom Pastuszek, executive director of Philadelphia Outward Bound School, as she led the way up the faded blue, 19th-century tiles that erratically pave the short trail through the woods to the wildlife-rich lake.

Suddenly, only a few hundred yards from 33rd Street near Oxford, a deep, serene silence engulfed the wooded lakeside trail, punctuated only by bird song.

Pastuszek said when she learned that the National Audubon Society wanted to partner with Outward Bound to reinvent the abandoned reservoir as a nature center for Philadelphia kids, she thought, "Somebody better pinch me. I'm dreaming."

She said Outward Bound's wilderness survival treks prepare teens to love and protect natural areas like Strawberry Mansion Lake, where Audubon Pennsylvania lifers like Keith Russell can lead bird-watching groups, as he was doing when Pastuszek encountered him on the leaf-strewn trail.

Russell, who initiated mid-winter bird counts here in 1987 and is a major player in encouraging Philadelphians to enjoy bird walks in city parks, said his group had spotted "pied-billed grebes hanging out with the geese" on the lake and a much rarer red-necked grebe, along with songbirds that like to live near water.

Tonnetta Graham, president of the Strawberry Mansion Community Development Corporation, said, "There was a time years ago when we were able to hike and jog around the reservoir.

"Then it was fenced off because of safety issues, and for generations, our community didn't know what [was] behind that fence."

Today, Mayor Nutter, an Outward Bound pioneer in Philly, will announce the new Discovery Center by attempting to climb a 30-foot, temporary rock wall at the lake.

Whether or not Nutter reaches the summit, his message will be cheered in Strawberry Mansion.

"We will again have access to a place that we've always felt was so tranquil in a park we've always loved and respected as our own backyard," Graham said.

"As neighborhood children, we all enjoyed getting a lot of scratches and bruises on those nature hikes up in there," she said, laughing.

"It's a natural area in the middle of Strawberry Mansion," Graham said. "And it's beautiful."

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On Twitter: @DanGeringer