HAMILTON, WASHINGTON

Karin Vail's modest white house near Washington's Skagit River seemed like a perfect choice when she bought it 22 years ago. She looked forward to raising her family on its spacious one-and-a-half acres. Now, however, she just wants out.

Vail, a resolute woman in her mid- 40s with long, curly red hair, stands on her shaggy lawn and gestures toward the Skagit, whose sandy banks lie about 1,000 feet away. On a mild day like today, the river slips peacefully by, but she knows all too well how menacing it can be.

"Every time it rains," she says, "you're stressing." At least five times since she and her husband, Brian, moved here, heavy rains have sent the river raging over its banks. After a 1995 flood, they raised the house on a 9-foot-tall concrete foundation. Then a 2003 flood dumped enough mud in their basement to fill 60 wheelbarrows. "Goopy, gloppy, sticky stuff," she says. "It's horrible."

Many of her neighbors' houses are also perched on stacked foundations, and attempts have been made to barricade the river with levees. But the most effective flood-protection measures have proven to be strict rules on reconstruction and a ban on new building enacted by the state decades ago, restrictions that apply only to a handful of the state's most flood-prone areas.

Now the National Wildlife Federation and other environmental groups want to see stronger development controls for more Western floodplains. It's increasingly clear that construction in floodplains is not only dangerous for people, it also harms habitat for salmon and other animals protected by the Endangered Species Act, including orca, Mexican spotted owls, jaguar and two species of springsnails. And the anxiety over floodplain construction is likely to rise as climate change raises flood risks.

So in courtrooms from Washington state to New Mexico, environmentalists have filed lawsuits challenging the flood insurance offered by the Federal Emergency Management Agency and related FEMA programs, which has helped Vail and her neighbors rebuild in a place that  is fundamentally unsuited for it.

If the groups succeed with FEMA, that will give them greater leverage over countless state and local policies permitting floodplain construction. They see their work as a smart strategy that can protect river ecosystems, safeguard residents, and spare taxpayers the expense of repairing flood damage. But they're up against strong opposition, including FEMA itself, as well as local governments and a building industry that want construction and the tax dollars that come with it.

The National Flood Insurance Program, the United States' largest backer of flood insurance, was founded in 1968 in an attempt to save taxpayers money by paying for damage with insurance premiums rather than emptying federal coffers. Anyone seeking a loan from a federally backed bank to buy or build in a floodplain must have flood insurance. In turn, the insurance is available only in cities and counties that agree to limit the likelihood of damage by restricting development in hazardous areas and elevating structures above expected flood levels. Local regulations help reduce risks, but can harm the environment.

Rocky bulkheads and levees straitjacket rivers, making them flow more quickly and washing away the gravel where salmon deposit their eggs. The barriers meant to hold back floodwaters also bar fish from habitat for feeding and reproduction. Mounding fill elevates the land in floodplains, but provides less space for floodwaters to spill into.

Development can also flush pesticides, oil and grease, and metals such as copper from brake pads into rivers. It also means that less water soaks into the soil to replenish the groundwater that feeds and cools salmon-bearing streams in Northwestern summers.

Floodplains are a sanctuary for salmon in high water. The water flows shallowly across the land, providing a calm haven with easy swimming and fewer predators. Young finger-sized fish thrive, gorging on bugs among the flooded trees and shrubs. Because floodplains are so important to salmon, long-term plans to recover the fish emphasize curtailing new development and encourage restoration of damaged areas.

In the Puget Sound region alone, more than 103,000 properties valued at $28.7 billion sit in floodplains. Homeowners and businesses hold more than 47,000 government-backed flood insurance policies, and FEMA has paid out approximately $240 million in flood claims in the past 34 years.

Nearly $4 million of those have been made in Hamilton -- an average of $33,700 per household. So many claims have been filed nationwide that FEMA has been forced to borrow from the U.S. Treasury. Before Hurricane Sandy struck this fall, the program was already about $17.8 billion in debt -- an amount that will surely grow as Sandy-related claims are settled.

Yet the number of building permits for floodplains continues to grow. It's difficult to predict how any single project might harm an ecosystem, but the fear is that each helps nudge sensitive species like salmon closer to extinction.

This has been the crux of the lawsuits filed against FEMA. In Washington, for example, the National Wildlife Federation is calling for better protection for salmon and orcas.

Development proponents are pushing back, arguing that not all construction in flood-prone areas is harmful. The suit, they claim, treats every floodplain in the Puget Sound region as if it's a pristine area that provides tremendous habitat value.

"Most of them are in fairly poor condition," says Molly Lawrence, an attorney for Property Owners for Sensible Floodplain Regulation. The alliance of industry groups and property owners has intervened in the case, saying that existing state and local laws already safeguard floodplains. "In terms of salmon habitat, they don't provide a lot. … Fish don't really want to end up in the parking lot of the REI office building in the Kent Valley."