When Carolyn Friedman, a resident of the Edgehill neighborhood, sets foot in the Southern Central Connecticut Regional Water Authority park, she enters what she calls a “microcosm of Vermont.” The black-eyed Susans are in bloom, and monarch butterflies flit among the butterfly weeds. The ponds below are lined with gum trees.

“I feel as if I am miles away from New Haven,” Friedman said in an e-mail.

But amid the natural setting there is a structure incongruous with the rest of the park, one that resembles a crashed spaceship. It is the Regional Water Authority plant.

The plant opened late last year, but it has taken that long for the park itself to open, after almost a decade of discussions and arguments that eventually led to a lawsuit brought by the cities of New Haven and Hamden against the water authority. The suit, which eventually settled out of court, was brought because the cities feared the water authority would go back on its verbal pledges to maintain the ecosystem of the area and to ensure that the RWA would not withdraw too much water from Hamden’s Lake Whitney reservoir. In the months since, however, local community leaders and the water authority appear to have found common ground.

From 1862 to 1991, the RWA operated a water filtration plant at the intersection of Edgehill and Armory roads. In 1997, the RWA began a dialogue with the neighborhood about the design of a new plant due to anticipation of increased water needs. Working with Edgehill residents and architects, RWA came up with a design that combined a state-of-the art water treatment plant with a neighborhood park.

Elizabeth Gilson, a resident of the neighborhood and one of the lawyers who represented New Haven and Hamden against RWA, said bringing suit was a way to ensure that the public had information about the potential dangers of the new water plant and to hold the water authority responsible for its actions.

“The plan is very detailed,” Gilson said. “As long as there are people still interested in it, we can monitor it. … [The RWA] can take the water they need and maintain the integrity of the ecosystem.”

The park is separated into seven landscapes: the south border on Whitney Avenue, ponds, the Eli Whitney barn, streams, gardens, a meadow, and a roof garden on the water treatment plant. Asphalt paths wind through the different landscapes. To reduce costs, the dirt from construction was turned into a wild-flowered covered hill. Nancy Ahlstrom, who served as the head of the park’s construction committee, said the hill ended up being a “very intellectual” feature of the park that models a natural precipitation pattern.

“It is a mountain clouds hang over,” she said. “The rain ends up in the ponds below.”

The landscape is designed to develop in a guided natural way and to transform over time. There are 21 species of native wildflowers and grasses and 100 different species of shrubs and trees, standing in stark opposition to the musket factory that Eli Whitney built on the site in 1798.

“It is a resurrection of the site before Whitney came,” said Bill Brown, director of the Eli Whitney Museum, which abuts the park.

The water authority’s original plan was to withdraw 30 million gallons of water a day from the Lake Whitney reservoir. But the plant that had previously pumped water from Lake Whitney had withdrawn an average of only six million gallons of water a day. In 1998, a team of scientists recruited by the RWA studied the potential effects of such a drastic increase in withdrawal on Lake Whitney and the Mill River — both parts of East Rock Park. The report concluded that such an increase in withdrawal could lead to stinking mudflats in upper Lake Whitney, massive fish kills due to inadequate water oxidation, and the drying up of a popular waterfall on the Mill River. In response, the RWA scaled down its withdrawal plan to 15 million gallons of water a day and assured neighbors that there would be adequate flow year-round.

Despite these promises, some New Haven residents still feared for the worst. In the 1990s, the state of Connecticut gave companies permission to withdraw water without any form of environmental restrictions as long as the companies registered the maximum amount of water they could withdraw. Several Connecticut municipalities were already suffering ecological damage because of this unrestricted withdrawal policy. A group of New Haven residents was determined to spare the Mill River and Lake Whitney from a similar fate, prompting the 1999 lawsuit.

In 2000 the two sides came to a settlement. The RWA agreed to a written Management Plan, which set operating procedures and monitoring measures to protect the health of Lake Whitney and the Mill River for the area’s wildlife. The Web site whitneydigs.com was set up by the RWA to inform the public about the plant, its construction, and the current health status and level of the Lake Whitney reservoir.

“You can’t see the absence of the fifteen million gallons of water,” Brown said. “It was the rational solution.”

The RWA also built an artificial waterfall in case the water withdrawals diminish flow over the Mill Rock waterfall. The artificial waterfall creates a thin curtain of water over the natural fall so that the waterfall is never completely dry.

When the water authority began to seriously consider opening the Lake Whitney plant again, the company decided to include neighborhood residents in the planning phases of the plant and park. They began holding meetings, and asked neighbors to elect representatives to work with the RWA in selecting architects for both the park and the plant.

Ahlstrom said the neighborhood was “very enthusiastic” about the park, and that being in the park is “like being in the country in the city.”

“The water company has done a terrific job,” Ahlstrom said. “It proves you can have an attractive water plant in a residential area that people like and not hate.”

The park’s design committee members traveled to New York City to interview Michael Van Valkenburgh, whose firm designed the landscape for the park.

“The design of the landscape of the Connecticut Water Treatment Facility is shaped and engineered to anticipate the dynamic interplay of water passing over and through the landscape,” the Michael Van Valkenburgh Associates Inc. web-site reads. “The project becomes an opportunity to engage in a joyous dance with nature, the choreography of which is designed, but the final outcome of the performance will be revealed over time.”

Ethel Berger, who lives six blocks from the park, said she “loves” the gardens, particularly the hill and the variety of wildflowers.

“I think it’s fantastic that the Water Company was willing to work with the neighbors, both in terms of architectural design and landscaping,” Berger said in an e-mail. “A lot of people worked extremely hard to bring this project to completion, and I think it is a wonderful example of a community working together.”

In contrast to the natural beauty of the park, the Water Treatment Facility is strikingly modern. Designed by Steven Holl Associates, the building is long tubular structure sheathed in stainless steel. The interior has curved walls and side and ceiling skylights. It houses the administrative offices of the RWA and the water-filtration plant. Elements of the design correspond to parts of the water treatment process. For example, the “bubble” skylight lenses mimic the oxidation of water.

Carl Gottschalk, the head of the Design Committee, acknowledged that not all residents of the area appreciated the design of the building as much as they enjoyed the park itself.

“When one goes for pure design, not a safe alternative, some people will be dissatisfied,” Gottschalk said. “I believe that [the Water Treatment Facility] will be a feature of the community and an icon for the next two hundred years.”