CINCINNATI (AP) — A beam of light illuminates the inside of a blue bucket.

There are dozens of them— more than 50 for sure —buried in holes along the wetlands and streams in a corner of Oak Glen Nature Preserve in western Colerain Township.

The buckets' rims are flush with the earth so that any little creature walking around can fall right in.

That's the point.

The buckets are for catching salamander— gunmetal gray Jefferson salamanders mostly.

These little guys will tell us how well the cleanup of 21,000 gallons of crude oil from a spill nearly three years ago is going.

It's oddly warm— nearly 60 degrees —on a Saturday night in early February.

What we need is rain.

We need enough to dampen the ground and tempt the nocturnal amphibians to head to the stream and wetlands.

Marching around in the dark and the mud our headlights wash over the contaminated land.

Off to the east, we hear a chorus of spring peepers— small tree frogs chirping in short, high-pitched whistles.

A wetland cacophony can get loud enough to hurt your ears, said Bret Henninger, natural resources director for Great Parks of Hamilton County, which owns and protects the preserve.

But this wetland in front of us, the one impacted by the spill, is deathly quiet.

Henninger can't say for sure that the frogs stay away because of the pollution, but as a trained biologist with 22 years at the park district, he'd bet it's the reason.

Moving along, pulling our boots out of the sucking mud, we check about a dozen buckets.

Nothing but leaf litter and some water.

It's still not raining.

We walk along the creek, noticing sheens on still pools that could be remnants of oil, Henninger says. Crude still seeps out of the earth when the area floods. Sunoco, which owns the pipeline, is called to clean it up.

Crews have found some salamanders in the buckets over the last couple of weeks, Henninger said. When found, they are documented and released.

The purpose is not to compare them to an earlier population estimate; Great Parks didn't have one. It's about figuring out whether the salamanders will return to the area.

"There might not be enough oil to actually kill them," Henninger said, "so the question is do the young ones survive?"

And, there might not be enough food to support their survival. Bugs and tiny invertebrates (salamander food) are more sensitive to pollution, Henninger said.

We see the lack of biodiversity first hand, flipping over rocks and scouring little pools we find little living in the reconstructed stream.

The most prevalent organisms are small white aquatic bugs, a cousin of the rolly polly.

In one spot, we find hundreds of these insects crowded on a few rocks.

"That's unusual," Henninger said. "I would say there are no other insect predators in there."

Park officials are hopeful the stream recovers and the salamanders will find it suitable.

The survey, which Henninger expects to continue for 10 years, should bear that out.

We trudge on, past a steep reconstructed stream bank that channels water toward the wetland.

The landscape looks eerily barren but is seeded with grasses and saplings that will hopefully take root.

The stream was flushed out after oil gushed from a crack that formed in the 60-year-old underground pipe that moves the fossil fuel from Texas to Michigan. Each rock was removed, cleaned and replaced.

Sunoco and its affiliates, including the pipeline operator Mid-Valley, agreed late last year to pay $923,000 to clean up the preserve.

What's a painful paradox is that Oak Glen is one of four conservation areas the county park system tries to keep untouched by humans.

On this night, we don't find any salamanders.

Not Jefferson or the even the more elusive and endangered cave salamander, which lives in crevices of limestone.

Our most interesting find is a horsehair worm, common aquatic worms that are often overlooked. Slender and cream-colored, it twists into a loose ball-shaped knot in my palm.

Cursing the clouds we say our goodbyes.

And, wouldn't you know it, as soon as the car picks up speed on Interstate 275, the rain comes down in droves.

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Information from: The Cincinnati Enquirer, http://www.enquirer.com