For nearly two centuries there has been a dam across the Des Plaines River in the area of what is present-day Riverside. Two weeks from now, the dam will simply be a memory.

Promptly at 7:15 a.m. on June 20, an excavator from Illinois Constructors Corporation scuttled across the shallow bed of the river, under the Barrypoint Bridge and onto a rock platform in front of the Hofmann Dam – the most recent structure, built in 1950.

Outfitted with a sledgehammer attachment, the excavator swung its arm into position and began chipping away.

Over the next hour, the excavator methodically pounded away at the center face of the dam, gradually opening up a notch through which water began to pour. By Monday a good 50 feet had been removed from the face of the concrete dam, and the water behind it had receded sufficiently to allow the excavator to work from either side.

“I’m sad to see it go, but if it improves Swan Pond or the river flow and stops flooding up river, it’ll be worth the eight or nine years it’s taken,” said Tim Forney, a Riverside resident for the past 41 years, who stopped by on June 20 to witness the dam removal process start.

While the removal of the dam is expected to have little, if any, impact on flooding, the main purpose of the project is to improve the ecosystem above the dam and eliminate a proven safety hazard.

Forney said he has canoed in the river above and below the dam and is looking forward to being able to paddle down the river unimpeded through Riverside.

“You get a nice view through here,” he said.

Lyons resident Bruce Von Ohlen, who lives in the Riverwalk Condominiums on the south bank of the river near the dam thinks the project is a bad idea.

“I think it’s a waste of taxpayer dollars,” Von Ohlen said. “There’s no reason to do it. It’s really quite a shame.”

Another Riverside resident, a woman who declined to give her name, said she’s a little nervous about what the removal of the dam will mean in the long run.

“I hate to see it go,” she said. “If it’s a positive, that would be great, but I’m not convinced. If there are negative effects, hopefully they can rectify them.”

She wasn’t the only person in Riverside afraid of the negative effects of the dam removal. Since April, residents who live along Maplewood Road have pleaded with village officials to pull their support for the project, claiming lower water levels might have a negative impact on their properties.

As the water receded from the banks upstream, the wide lagoon behind the dam disappeared, revealing wide mudflats, particularly on the Lyons side of the river. But the water receded far upstream of the dam, exposing the banks at the Forest Avenue bridge and points north along the borders of the properties on the west side of Maplewood Road.

The receding water also revealed a part of Riverside and Lyons’ distant past. Remnants of an older dam were exposed as the water leveled off – its shape clearly visible just west of the newer dam.

Just what that structure is, officials are unclear. It could be remnants of George Hofmann’s 1908 dam, or it could be remnants of the dam built of stone and timber in 1866.

And it’s still performing its old job pretty admirably, slowing the flow of water downstream. A capsized metal rowboat emerged behind the horseshoe dam as water rushed through the channel opened up in the middle of the newer dam. Between the two structures, various pieces of other debris – from car tires to a large storage canister – also appeared.

All of the debris and the remnants of the old dam itself will have to be removed by the U.S. Army Corps of Engineers as part of the scope of work, said Jeff Zuercher, project manager for the Army Corps.

“There is a line item for the removal of the legacy dam and debris,” said Zuercher. “We anticipated there would be a need for this. We’ll work with the contractor to get all of the debris out of there.”

On Monday, the removal contractor poked at the legacy dam remnants and reported that it was pretty fragile. The structure is between two and three feet high, said Zuercher.

“It fell apart pretty easily when they grabbed at it,” Zuercher said. “It will help facilitate good, clean river passage by getting that out of there.”

As for what will happen to water levels when the older structure is removed, Zuercher said it will have some effect, but not much.

“We expect it to drop some, but we’ve seen the major change,” he said. “North of Forest Avenue, there may be no change at all.”

While that determination is made, the Army Corps will continue to remove the straight dam. Work will continue toward the Riverside side of the river. When the excavator reaches the end point there, it will swing around and turn its attention to the dam going toward Lyons.

When work is complete on July 7, weather permitting, the center 150 feet of the concrete dam will be gone, removed all the way to bedrock and the water will seek the natural channel of the Des Plaines River, one that hasn’t been seen much since 1827, when the Laughton brothers built the first dam for a sawmill atop a natural waterfall.

That dam was rebuilt several times, first in 1866 and then in 1908 by George Hofmann, who constructed a horseshoe-shaped dam to create a pool of water to be used alternately for recreational purposes and to supply electricity to his adjacent recreational park in Lyons.

What Hofmann’s dam actually succeeded in doing was to create an open sewer behind it. When Hofmann ignored complaints about the pollution, the Sanitary District of Chicago in 1928 built a bypass on the Riverside side of the river to wash the pollution downstream.

In 1950, after deterioration of the top of the horseshoe dam had dropped water levels to near bone-dry, the state of Illinois replaced it with the present dam.

Storm water runoff due to increased urbanization and the influx of water from 11 treatment plants upstream of Riverside have significantly increased flows in the Des Plaines since 1950, say officials, making it far less likely to experience the kind of low water levels seen at that time.

Still, the low water levels seen in the immediate aftermath of the dam’s notching were somewhat startling, despite the fact that everyone knew the water would drop significantly after the dam was gone.

The drought-like conditions have not helped, said Zuercher.

“We’re not really surprised, expect that we’re in the middle of a drought and this is one of the lowest levels we’ve seen in the last decade,” Zuercher said. “It’s really great for construction, but we’re already exposing the banks at our worst-case scenario. It can only get better from here.”

Zuercher said that the company contracted to replant the banks of the river upstream of the dam will begin their work this week. In addition to laying down erosion-control mats, crews will begin to plant thousands of seeds and plant plugs on the exposed banks.

“In some areas that were exposed, we did see plants starting to grow. Some stuff did start to sprout,” Zuercher said.