Just off of High Street in Pottstown, Pennsylvania, the Manatawny Creek flows freely. But for more than a century, this spot had been stopped up by an 8-foot tall dam which shaped the creek into a pond at nearby Memorial Park. According to Bill Cannon, with the Greater Pottstown Watershed Alliance, no one can remember why the dam was built in the first place.

"There's been various theories... one was that it was an ice dam to create during the wintertime... ice behind it... the ice would be cut up, stored, and then sold during the warmer climate."

Long after the advent of refrigeration cut back on ice-sales, ice was still backing up at the dam. John Erskin lives near Memorial Park. He says a major storm about four years ago caused thousands of dollars of damage to the park when ice moved up the creek banks.

"The impoundment was frozen and we had a flood, and it lifted everything up and we had quite a bit of damage. I mean when it was done there was just huge slabs of ice just laying all over the ballfields there in Memorial Park."

The state considered the Manatawny dam orphaned. Nobody owned it, and no one was willing to take responsibility for the damage. The dam no longer served any purpose; it was causing problems for the park, and in the summertime, children would sometimes swim in the creek, where they could get caught in a dangerous undertow created by the dam. So the Pottstown watershed group scrounged up some grant money to take the dam out.

Before, during, and after the dam came down two years ago, 30 researchers from the Academy of Natural Sciences in Philadelphia spent time at the site. According to lead researcher David Hart, few projects have taken such a comprehensive look at the ecological impact of dam removal.

" We measured whether there were heavy metals out there, whether there were other kind of pollutants that might be present. Biological measures of the health of the ecosystem. What types of algae, what types of inverterbrates crawling around, little insects that fish like to eat. And then studies where we tagged individual fish and tried to find out what they'd do when the dam is removed."

Hart says it's also important to predict what the dirt, gravel, and other possibly contaminated residue piled up behind and old dam might do once the obstruction is removed. But since the Manatawny Dam was removed, Hart says the biggest change is that the local ecosystem is returning to a river habitat, after spending more than a hundred years as a lake-like environment.

"Many of the fish species that were present in the ponded area upstream of the dam, species like carp and goldfish have now become less abundant and instead what we're seeing is more of a typical river fish fauna, things like rock bass and other species that are now more common than they were in the past."

While some neighbors were sad to see the pond go, Manatawny Creek hasn't flooded since the dam was torn down, and according to the watershed alliance's Bill Cannon, fishing on the creek has picked up a bit.

Cannon says there are thousands of unnecessary dams throughout the United States, and removing the Manatawny dam restored a bit of nature to urban Pottstown.

"It's kind of tough to have a perfectly natural state when you're surrounded by bridges and walls and buildings, but we're trying as close as we can get."

The results of the Academy's study have been presented across the country and could assist other communities looking at similar projects. Scientists plan to continue visiting the site as long as possible to evaluate the long term effects of dam removal.

More information is available on the web at GreenWorks.tv. I'm Brad Linder.