The golden rule of wetlands, as every developer knows, is that if you destroy or alter them, you must replace them.

It's a practice known as wetland mitigation, and there are federal and state laws that govern it - the federal Clean Water Act is a major one. Those statutes apply equally to private companies and government agencies.

A few years back, the county acted on a federal requirement and expanded an airport runway. In the process, the county disturbed nine acres of wetland on the site. The impact couldn't be avoided, so the county built a new 13-acre wetland in Chili's Black Creek Park to offset the loss.

The county is now evaluating the prospect of building a wetland mitigation bank. That would be a multi-acre collection of manmade wetland, proactively constructed to offset wetlands lost because of future county projects.

But natural wetlands are where they are for a reason; they're often formed over centuries because of specific natural and physical factors. So when it comes to the effectiveness of manmade wetlands, like the mitigation bank the county's exploring, there are some skeptics in the environmental and natural sciences communities.

"I think the science would show that if you're creating a wetland on an area that's never been wetland, you're going to have trouble," says Jim Howe, executive director of the Nature Conservancy's Central and Western New York Chapter.

Restored wetlands typically come back very fast and have the same functional values that the wetlands previously had, Howe says. An example would be restoring a farm field that was drained from wetlands by removing the drainage system.

Wetlands are complex ecosystems with an equally complex set of defining criteria. There are different types - marshes, swamps, bogs, and others - but they do have common features like prolonged flooding and wet soils, says a fact sheet from the state Department of Environmental Conservation. Wetlands filter water, provide habitat for numerous species, and provide flood protection, among other important ecological benefits.

The performance and functions of the artificial wetland in Black Creek Park are improving, says Larry Staub, the county's parks director. The county's still tinkering with the design and is monitoring the progress, he says.

"It's something that's new and interesting," Staub says. "It's become a haven for wildlife out there, from waterfowl to fox, and we've had sightings of great egrets out there, which we've never had at Black Creek Park."

Scott Jones, a wetland biologist for the regional DEC office, says the project, while improving, has struggled because the site doesn't have enough natural water.

The county is exploring mitigation banking to offset wetlands lost during future projects, namely those at the airport and the Mill Seat Landfill, Staub says.

The project would not focus on mitigating privately-disturbed wetlands, Staub says. Some in local environmental circles are afraid that the county could establish a bank in a park and then sell acreage to private developers who need to mitigate a project.

County officials haven't selected a location yet. They've advertised for a consultant to perform a feasibility study and to help evaluate potential sites. Proposals were due on October 16.

Both the airport and the landfill are on the county's west side, and both are in the Black Creek watershed. To comply with wetlands regulations, the mitigation bank would lie within that watershed as well.

"It all has to do with soil types and the hydrology," Staub says.

The county has had discussions with the state DEC Region 8 staff about using a 25-acre parcel in Black Creek Park's south end for the mitigation bank. After DEC staff inspected the site, however, they told the county that the site didn't look promising. There aren't enough former wetland areas, which would make it harder for new wetlands to take, the DEC's Jones says. Department staff encouraged the county to look at other sites, and provided a couple of leads.

The wetland project in Black Creek Park is as an example of the difficulty the county would face building a bank in the park, Jones says. It's on the park's north side, next to DEC and Army Corps of Engineers wetlands. But it's in a drier area. Both Jones and Staub say the project's about halfway toward meeting its goals.

"That's been an ongoing problem for them and they're looking for fixes to that one," Jones says. "Why would you go try to do a bank in an equally challenging area?"

If the county were to build a bank, it would be under the regulatory authority of the DEC and the Army Corps of Engineers, as well as other federal agencies.

Developing a new wetland isn't as simple as picking a site and flooding it. Their complex ecosystems are maintained through a sensitive balance of different features. And getting that balance correct can take a lot of time and work, if it's achieved at all.

In 2006, the state of Ohio's Environmental Protection Agency studied the performance and success of its wetland mitigation banks. It concluded that approximately half of the state's mitigation banks were underperforming. For example, none of them provided habitat for sensitive yet critical frog and salamander species, says a report, and they generally had poor amphibian communities.

The blame, the report says, falls on a combination of poor design, planning, and management.

"What is needed is a re-appreciation that this is not easy work, that the devil is in the details at all levels, and that nature does know best (or at least is our best referent for success)," the report says.

The report's authors did say that manmade wetland mitigation banks can be successful in the long term, as long as they are sited, built, and managed properly.

Too, grouping manmade sites together has a couple of significant advantages. For one, pooling together multiple mitigation projects into one location makes monitoring and regulatory enforcement simpler - an important consideration given the dwindling numbers of DEC staff. Monitoring provisions are built right into both DEC and Corps of Engineers permits.

The banks also lead to more effective, successful mitigation projects. They help avoid a "puddle effect," where there are small, isolated projects that may filter water, or serve as a landing pad for geese, but have little other benefit.

"It makes sense for Monroe County DOT, Monroe County parks, the airport," Jones says. "These types of agencies are going to have projects that may require mitigation and having a mitigation bank up and running keeps them from having to reinvent the wheel with every permit application."

Wetlands mitigation banks are relatively new in New York. Rochester's Cornerstone Group, a private development company, opened the state's first bank in 2001. It's a 20-acre site located in Chili, on the southern side of the Rochester International Commerce Center.

Cornerstone pursued the idea of a mitigation bank out of recognition that building wetlands can be a complicated and expensive proposition, says Roger Brandt, the company's president. He tells the story of a former partner who had to buy three to four acres of land to offset wetland impacted during a project. The developer had to get regulatory approvals for the work and also had to put up money so that, if the project failed, the Army Corps of Engineers could fix it. [Disclosure: the Cornerstone Group is part of a team that's submitted a proposal for the county's mitigation bank project.]

It took three years for Cornerstone to get approvals for the mitigation bank from a handful of state and federal agencies, and they started selling acreage in 2001. Most of the developers who have bought credits have had projects that impacted small amounts of wetland.

"We took all of the risks," Brandt says. "If it doesn't work, it's our fault. You get your project taken care of."

The wetland functions well, he says. When the Corps of Engineers and the EPA inspected the project two years ago, they gave it high marks.

"One of the keys was, number one, the hydrology, and number two, the location," Brandt says. "We're over by the airport, backed up next to the railroad tracks, which contains an awful lot of wetlands."

The site has more than 100 varieties of wetland plants and attracts turtles, green herons, great blue herons, and a number of frog species.

"Once it took off, it was terrific. It worked out real well," Brandt says. "It's a very lush area now. It's fun to be over there when a big rain is occurring or has occurred. You see the water kind of picking up and moving."