Deep in Cape May County lies a scene that has changed little in almost 330 years. Lilies float on the surface of Magnolia Lake, its waters reflecting the distant trees that line the banks. And the traffic that sometimes backs up on Shore Road does so on a dam that has held back these placid waters since 1684.

The 750-foot Magnolia Lake Dam is the oldest dam in the state, according to records with the state Department of Environmental Protection and the U.S. Army Corps of Engineers. It is one of eight similar structures around New Jersey that pre-date the founding of the United States.

While engineers believe these structures are sound, the state is upgrading them one at a time because they pre-date current standards. Tim Morris, the director of hydraulics and dam engineering for the statewide engineering firm Cherry, Weber & Associates, said, "When the dams were built 250 to 300 years ago, (people building them) had no background in rainfall and flooding."

The state has regulated dams since 1912, said John H. Moyle, the manager of the DEP's Bureau of Dam Safety & Flood Control. That agency oversees about 1,600 dams, DEP spokesman Bob Considine said. The U.S. Army Corps of Engineers also identifies the state's 826 most significant dams in its National Inventory of Dams program.

Studies have shown that dams are most likely to fail in their initial decades, Morris said. Over the years the soil in these older earthen dams compacts and essentially becomes a part of the landscape. He said, "The earthen embankments on the older dams are as sound as you could hope for."

State regulations specify many construction and maintenance issues, as well as the minimum-strength storms that dams must withstand. These minimums vary depending on county, location and size of dam. Morris said standards have increased in recent years, as state scientists adjust for climate change.

In 2005, the state Department of Transportation began a $5.5 million project on the Lake Pohatcong Dam in Tuckerton. The 670-foot dam was widened by 30 feet in 1931. The current project is designed to replace and upgrade the spillway and outflow pipes to enable it to handle larger storms.

Similar work is planned for the Magnolia Lake dam, Morris said. In November, waves from Hurricane Sandy pushed water up the bay, through Mill Creek, across Route 9 and over the top of the Magnolia Lake Dam.

When the water washed back into the sea, it took part of the sluice gate with it, said long-time resident James Waltz, 85. He said the level of the lake suddenly fell by two and a half feet.

"We were pretty much worried about it," Waltz said.

After a Navy reconnaissance blimp found the mostly drained lake, Waltz said, crews arrived from the owner of the dam, the state Department of Transportation. A little more than a week later and the temporary construction was done: a new concrete base from the lake to the sluice gate. Within days, the water levels began to rise.

This dam, like many others of the state's oldest, was originally built to power a mill. Its founder was John Townsend, who built an adjacent home, harnessed the waterpower to initially saw wood, and then grind corn and grain.

And then, about 100 years ago, current resident Alma George said, her great-grandmother used it to power a small factory to can tomatoes. Today the mill building and 1680s-era home both still stand next to the historic dam.

"I live in a little piece of history," George said.

Many of these older dams survived for two reasons, Morris said: "Either they were out of the way or (someone) built a road over them."

If these dams were remote enough, Morris said, they were never destroyed by later development.

And once these dams were in place, they quickly became a convenient way to cross from one piece of dry land to another, in otherwise marshy terrain. Over the years, these narrow footpaths grew, were widened, then paved, and now hold important local roads.

Today, U.S. Route 9 runs across the top of the state's only two confirmed pre-1700 dams, at Magnolia Lake and at Lake Pohatcong in Tuckerton. Isolation may be why rural Dennis Township is home to three of New Jersey's 11 oldest dams, at Magnolia Lake, Johnson Pond and East Creek Pond.

"Well, I don't know if it's necessarily surprising," that these old dams were there, Dennis Township Mayor Eugene L. Glembocki said. "We are a fairly old town."

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New Jersey's oldest dams

* Department of Environmental Protection records list the dam as being completed in 1931. Older DEP records indicated it was constructed around 1680 and later widened by 20 feet in 1931. Tuckerton Historical Society curator Barbara Bolton said it was built no earlier than the 1690s.