CORVALLIS, Ore. (AP) - Pioneers risked everything to reach the flat, fertile soil of the Willamette Valley, then and now some of the best farmland anywhere.

Today commercial interests value the undeveloped flatness for factories and warehouses.

But there's a catch.

Each site has to be checked for the presence of wetlands, protected by state and federal law.

John Pascone, president of the Albany-Millersburg Economic Development Corp., calls the issue a "hidden minefield" because a lot of wetland acreage was converted to agricultural use long before laws protecting it took effect.

Sometimes developers can build around wetlands. If not, they can agree to offset, or mitigate, development impacts by creating new wetlands or buy credits in offsite mitigation banks to stop wetland losses. The going rate in the valley now is between $65,000 and $90,000 an acre.

The Lowe's Distribution Center in Lebanon and the planned PepsiCo fitness drink factory in Albany paid for mitigation work.

But smaller companies can't afford it, and some larger ones will go elsewhere rather than deal with mapping delays and waits for permits.

Growth in the valley is making the problem worse,

"We're going to reach a point where there's no land to mitigate on," Pascone predicted.

Residential developers also are affected.

K&D Engineering President Dan Watson, who serves on the boards of both the state and local homebuilders associations, said wetland-free property in the valley is scarcer and wetland definitions are getting more strict.

"Today I can't tell a wetlands from a ryegrass field. I have to hire a wetlands consultant to help me figure it out," Watson said.

Increasing similar complaints has prompted mid-valley officials to try a new approach.

In April, a committee representing Corvallis, Albany, Millersburg, Lebanon, Tangent and Harrisburg will try to find a regional solution, which could include rezoning industrial lands to make more wetland-free property available for development.

Communities could agree to preserve high-quality wetlands on industrial-zoned land while designating other vacant property for development.

Many potential developers have learned the hard way that much of the Willamette Valley is wetland, which they didn't know by looking.

"A whole lot of wetlands are seasonal, and they don't look like wetlands during the summer and fall," said Janet Morlan, wetlands program manager for the Oregon Department of State Lands.

Many seasonal wetlands are planted to ryegrass, which does well in the alternating wet and dry conditions.

There are no problems if wetlands are used for farming. Development is another matter.

Those rules rarely prohibit construction outright, but mean a lengthy, expensive permitting process.

Many see wetlands as open-water marshes dotted with cattails and bullrushes, Morlan said. They're often surprised to learn that ryegrass field that are firm and dry in September are wetlands when the rains start and may provide important "ecosystem services" such as flood control.

"I use the analogy of a sponge. If you're going to use a sponge, you wring it out first," Morlan said. "It's the same thing with a wetland. If it's always full of water, it can't absorb more."

But landowners sometimes feel they're the ones being squeezed.

Albany's Henshaw Farm, a proposed subdivision, was scuttled because of wetlands restrictions.

A Portland development group, Wellner Morey, bought the 182 acres of farmland in early 2006 for $2.2 million, with plans to build 429 homes. The Albany Planning Commission approved if wetlands standards were met.

There were some identified wetlands on the site but the company didn't reckon on a huge swath of grass seed field on the property that was converted wetland that couldn't be developed without extensive and expensive mitigation work.

In the end the company walked away from the deal.

Maps based on aerial photos detect all wetlands, but because working farms are exempt, the national wetland inventory doesn't map them.

But Morlan says problems aside, the ecosystem services wetlands provide, from flood control to wildlife habitat and more benefit everyone.

In a study of land use changes from 1982 to 1994, Morlan and fellow researchers found that the valley lost an average of 546 acres of wetlands each year despite restrictions.