UNION COUNTY — Lake Surprise got its curious name because the manmade pond, built in 1845 in the Watchung Mountains, was practically invisible until you were right next to it. This summer, it might be even harder to spot.
Union County is draining the water from the lake — all 23 million gallons of it — to construct a new dam, replacing the century-old structure situated on the far end of the narrow basin.
Parts of the current dam date to when David Felt first constructed Feltville Lake, as it was then known, to help power his mill. It has been updated in bits and pieces since, according to the county, but this is the first complete overhaul.
According to county officials, the current dam leaks 1,500 gallons of water every day.
But before they can begin construction, officials first opted to lower the lake, which they said made the project safer for construction crews. A county engineer compared building a dam on a full lake to a “loaded gun.”
The first step in that process was to remove the fish from the lake — a small crew set out to do that in late May, trawling through the water and using “electrofishing” to zap and safely retrieve as much of the lake’s fish population as possible. Those fish were then moved to other lakes in the county.
Last week, engineers used hydraulics to suck out most of the water and pump it downstream into the Blue Brook, a county engineer said. Officials said they don’t expect the extra water, or temporary lack of dam, to have any significant impact on the brook.
An electrofishing crew will soon return to take the last of the fish, and then the rest of the water will be removed.
Officials said they considered removing the dam completely. But since the lake is man-made, removing the dam would eventually let it return to its natural state as a portion of the Blue Brook tributary, and officials scrapped that idea, citing the lake’s popularity with visitors and hikers.
A dam at Seeley’s Pond, downstream from Lake Surprise, will also be repaired as part of the same project.
The biggest concern for the county was overtopping, when water rushes over the top of the dam during a serious storm. Both dams will now comply with the Department of Environmental Protection’s Bureau of Dam Safety and Flood Control’s Dam Safety Standards.
“The cost of the dam repairs is minimal when compared with the economic consequences of a dam failure,” officials said in a post to the county website.
Belleville-based Ritacco Construction Company won a bid to build the dam, which will cost the county $3,608,000 — the lowest of 12 offers, according to Union County officials. The new dam will replicate the look of the current structure, using concrete as a base and stone masonry facing the trails that run through the area.
Though there is no set timeframe, officials hope that draining the lake now will allow them to complete construction before winter, and then allow the lake to refill by next summer.