The Susquehanna River seems to speed up as it thunders over the brink and jumps 55 feet down the face of Holtwood Dam.

Despite its eternal rush, the water always leaves behind baggage.

Michael Helfrich hiked the York County shoreline on a recent wintry day and stooped to study the latest deposit. His shoes sank in over their soles.

"There's some sediment for you," he said. He found a stick in the woods and tested the goo's depth: six inches.

Helfrich, the Lower Susquehanna Riverkeeper, nodded to where slushy ice plates stole by on the current. Much more silt lies unseen in the depths behind the dam, he said.

It's the same story at Safe Harbor to the north and Conowingo, roughly five river miles south of the Maryland line. The northern pools are already filled with gunk.

An average of two million tons a year are settling out behind the mile-wide Conowingo, which will reach capacity by 2025 or 2030, unless another Hurricane Agnes sweeps through.

The question of what to do with the accumulation — dredge it? ignore it? –—has hung unresolved for years.

Scientists started scrutinizing the river's sediment at least as far back as the 1960s. Political regulators and the utility companies that own the dams have been gridlocked over the problem ever since.

But silt is getting serious attention for the first time since 2001, now that the government is cracking down on Chesapeake Bay pollution and preparing to relicense Conowingo by 2014.

Two million federal dollars have been earmarked for a matching grant that would require Pennsylvania and Maryland to each pony up $250,000 for a comprehensive study of sediment transport.

A revived "sediment task force" aims to launch a research effort featuring new-generation computer modeling technology by Oct. 1, said Anna Compton, a biologist with the U.S. Army Corps of Engineers in Baltimore.

Meanwhile, Helfrich pointed out, Conowingo remains the bay's greatest benefactor because it annually traps about two-thirds of the river's sediment load.

But the dams also represent the bay's biggest threat.

In 2008, according to Susquehanna River Basin Commission estimates, 92 million tons of sediment lay stacked in Lake Clarke, behind Safe Harbor Dam. Fourteen million tons were bottled up behind Holtwood, and 174 million behind Conowingo.

All that trapped muck makes the river a cocked hammer waiting to be released by the trigger of a big storm.

The time to act is now, said Helfrich, who is affiliated with the Waterkeeper Alliance headed by Robert Kennedy Jr.

"A major scouring event could wipe out a lot of the work we've done" since Agnes struck 38 years ago.

Dirty solution
The Susquehanna, like all rivers, carries a natural burden of erosion-generated sediment. Storms have always scoured buildups into the bay.

But human activity has vastly altered what Helfrich calls "the grand gorge of the East Coast."

The two mighty dams off Lancaster County shores, Safe Harbor and Holtwood, were erected, respectively, in 1931 and 1910.

The 104-foot-high Conowingo Dam was completed in 1928.

Earlier, local settlers built hundreds of small grist mill impoundments that transformed stream valleys and laid down the so-called "legacy" sediments that still cloud modern waters.

In the early 20th century, Helfrich said, loggers leveled northern Pennsylvania forests, hastening runoff and boosting the river's annual silt burden to 10 million tons. The present load of roughly three million tons is "a lot better than [in] the days of out and out timbering."

Fish and plant life has nontheless withered under a barrage of mud and excess nutrients.

The nutrients ignite algal blooms that suck oxygen from the water and turn half the bay into a dead zone every summer. The trends are not promising.

The river already delivers to the estuary the equivalent of 7,000 dump truck loads of dirt per day, according to Chesapeake Bay Foundation scientist Harry Campbell. Now, he added, changing climate patterns are pounding the region with "more intense rains over shorter periods." Development is relentlessly expanding the land area capped by impervious surfaces. "We're seeing more erosive flow."

Helfrich often sees the results in the river. "When it's raining," he said, "everything is dirt brown."

Helfrich and Campbell favor streambank fencing and other measures to muzzle pollution from farms, lawns, sewer treatment plants and industry. They disagree — respectfully — on what to do with existing sediment.

Helfrich advocates dredging some of the muck, dewatering it and using a kiln to bake it into building material.

The costly "money pit" project would be impossible without public/private partnerships, admits Helfrich, who has explored the idea with HarborRock in Glen Mills.

Last summer, the for-profit company was given a Maryland Port Administration contract to determine if it's feasible to convert dredgings to lightweight aggregate.

Cutting pollution alone won't bail out the bay, Helfrich contends. Storms or no, Conowingo pool will eventually silt up. And then, according to U.S. Geological Survey predictions, the river will push 250 percent more sediment and 40 percent more phosphorus into the upper bay.

Coal dredging was a common practice on the Susquehanna before Agnes rearranged the riverbed; the waste anthracite particles that had floated down from northern mines were gleaned from the deeps and sold for fuel.

Now, though, the prospect of subtracting sediment stirs up sticky questions. Where would you base such operations. asks Tom Beauduy, SRBC deputy director? How much reserve capacity should there be? How many PCBs and other toxins lie buried in the muck?

"You could never take out all the sediment that is there," added Beauduy, voicing a consensus view.

Campbell considers dredging "putting a Band-Aid over a gunshot wound."

The submerged deposits would be hard to reach. Disturbing them would release phosphorus and imperil marine life, Campbell predicted. Nor would it address the nearly 16,000 miles of Pennsylvania streams already impaired by sediment and other pollutants.

The decision on dredging, if one is ever made, remains far off.

For now, regulators are working out who should study what. Even that picture is muddy.

Utility companies contend they aren't responsible for sediment, most of which originates elsewhere in the 27,500-square-mile Susquehanna watershed.

River advocates counter that the stuff would have been distributed gradually had the impoundments never been built.

PPL Electric, which owns Safe Harbor with Constellation Energy in Baltimore, has already been relicensed and will address sediment questions as required by the Federal Energy Regulatory Commission, PPL spokesman George Lewis said.

FERC has extended Holtwood's operating license through 2030 as part of a $440 million expansion plan that includes building a new power generating house, Lewis added.

Exelon Corp., which owns Conowingo and the Muddy Run Pumped Storage Facility, aims to research the impact of hydropower operations on sediments near the dams, said spokesman Bob Judge.

But SRBC officials want the company to also analyze underwater terrain far out in the bay.

The commission has notified Exelon that it's overseeing license approval in conjunction with FERC, said SRBC water resources management chief Mike Brownell. Exelon has appealed.

"There's some legal wrangling going on," Brownell said dryly.

He sees the bay and its tributaries as an integrated system that should be studied as such.

The network encompasses the silt-stuffed pools behind Holtwood and Safe Harbor, emphasized SRBC spokeswoman Susan Obleski – and, by extension, all river users, including the City of Lancaster, which she said seeks to nearly double its water intake from the Susquehanna.

Step one in sizing up sediment would be to create detailed bottom contour maps using sonar and GPS, Brownell said.

The USGS started that boat rowing with a 2008 bathymetric (bottom graphing) study of the riverbed, noted Brownell, who added that scientists are learning about the nature of the Susquehanna's gunk.

"It appears we're seeing finer material move over the dam" while sand and pebbles fall out of solution, he said. That starves the river for sediment and changes the ecology below the reservoirs.

How cataclysmic events impact the ecosystem is less well understood.

Flooding from Agnes pumped 20 million tons of goop into the bay, devastating the environment.

Ice jams from the fast-melting blizzard of 1996 released half that amount and resulted in much less damage.

Storms during the growing season pack a more lethal punch, according to Beauduy, who added that society's ability to forestall acts of nature is limited.

"You can't manage colossal floods," he said. "You're always going to get a certain amount of scour."

But that's why it's wise to try to limit the impact of the mudslide as much as possible, Helfrich said. Back along the bank of the Susquehanna, he scraped mud from his shoes.

Earlier, an immature bald eagle had launched from a tree branch. The gelid water roared as it arced over the Holtwood Dam breast.

"The canary's singing," Helfrich said.