Jeff Heuwinkel, 28, of the District photographs “the awesome power of water” in Potomac, Md., at the C&O Canal National Historic Park. After Hurricane Sandy, the Potomac River exceeded flood stage. (Katherine Frey/The Washington Post)

At her small beach house that sits in a flood zone, Nancy Loft-Powers worries. The prospect of rising water, she said, isn’t what bothers her. It’s the expected rise in the cost of her $7,500 yearly flood insurance.

“My insurance is more than my mortgage,” Loft-Powers said in a phone interview from her year-round home in Deerfield Beach, Fla., near Fort Lauderdale. “I live by the beach in an old neighborhood. I pay [too much] insurance for a crap house that’s not great.”

This April Fool’s Day, when a congressional act that revised federal insurance premiums goes into effect, coastal homeowners such as Loft-Powers say the joke will be on them. The government is slowly phasing out subsidized flood insurance for more than a million Americans with houses in flood zones who, in some cases, pay half the true commercial rate.

Some owners say they are angry because their houses near lakes, rivers, bays and oceans were much more affordable with cheap rates that will now increase by as much as 25 percent each year until the premiums equal the full risk of settling down on property mapped as a flood zone.

Congress ordered a rate increase because the National Flood Insurance Program (NFIP) managed by the Federal Emergency Management Agency is $24 billion in debt. It reached that historic amount because revenue from the discounted premiums could not cover payments on flood claims, particularly after two devastating hurricanes, Katrina and Sandy, on the Gulf and Atlantic coasts.

A large crowd gathered on the corner of King and Union Streets in Old Town Alexandria in anticipation of very high flood waters after Hurricane Sandy. (Tracy A. Woodward/The Washington Post)

Ninety percent of disasters in the United States result from flooding, according to NFIP statistics, and coastal homeowners with discounted policies are getting little sympathy from conservationists and advocates for taxpayers who think they should pay dearly for that risk.

Rising sea levels from climate change make coastal living even more dangerous, conservationists say. And the flood-insurance program that went into the red paying flood claims is deep in debt to a U.S. treasury funded by taxpayers, advocates say.

“Realistically it’s not great for people,” said Shannon Hulst Jarbeau, assistant director of a nonprofit group called Wetlands Watch in Norfolk, a low-lying city that struggles with flooding from sea-level rise. But the rate in­creases are “not so horrible either,” she said.

“These reforms need to happen. The rate increases drive an interest in adaptation to sea-level rise. It makes people start to understand the value of reducing flood risk because it hits them right in their pockets.”

A Government Accountability Office report last year said FEMA’s debt to taxpayers is so large that the agency can only afford to pay on its interest. It hasn’t made a principal payment in years. The NFIP collected about $4 billion in premiums in 2013 while insuring property worth nearly $1.5 trillion, the GAO said.

As the seas rise by a few millimeters each year, storm surge from hurricanes will only worsen. A study by the National Oceanic and Atmospheric Administration last year said long-term sea-level rise has made tidal flooding a near-daily event in many cities, as opposed to 1950, when it happened about once every two years.

Alec Howard, 6, of Arnold, Md., explores the flooded City Dock in Annapolis. (Marvin Joseph/The Washington Post)

The cost of bailing out the victims of Katrina and Sandy was so overwhelming that Congress passed the Biggert-Waters Act of 2012 that increased flood-insurance policies by 25 percent across the board for people living in flood zones. Much of it would be phased in, but new buyers of homes in the zones would absorb the full increase.

But that get-tough measure set off a panic in the real estate industry as home sales fell through because lenders refused to back prospective buyers because they couldn’t afford the insurance.

Deborah Baisden, president of the Virginia Association of Realtors in Richmond, said 1,300 real estate transactions a day were delayed when Biggert-Waters went into effect, threatening the housing recovery.

Loft-Powers, a chiropractor who wanted to invest in real estate, said she was forced to sell two homes she owned in Deerfield Beach at a greatly reduced price because she couldn’t cover the insurance payments in a state where four hurricanes — Charley, Frances, Ivan and Jeanne — hit over six weeks in 2004.

Under Biggert-Waters, her rate was set to increase about 25 percent with her yearly renewal. “I was devastated. I couldn’t take it. I had to short-sell a house. I didn’t make money,” Loft-Powers said in a stream of punctuated shouts.

It was exactly the kind of negative reaction insurance experts warned against before Congress passed the law, said J. Robert Hunter, director of insurance for the nonprofit Consumer Federation of America and a former federal insurance administrator who helped set government ­flood-policy rates in the 1970s.

After finally getting the message, it passed the Homeowner Flood Insurance Affordability Act of 2014 that revised the increase. Of the million Americans with subsidized flood insurance, about 800,000 primary owners live in their homes year-round, and 200,000 secondary owners rarely occupy their homes.

Businesses and nonresidential dwellings such as churches and farm buildings round out the remaining 100,000, according to FEMA.

Under the new law that goes into effect Wednesday, primary homeowners would see an average yearly 10 percent increase. Loft-Powers would pay an extra $750. To make up for slowing the revenue stream meant to pay FEMA’s debt to the U.S. treasury, primary residents living like her would pay an extra $25 yearly surcharge.

Secondary owners of vacation houses and condominiums will see about an 18 percent rate increase, along with a $250 yearly surcharge. Businesses and farms will also shoulder that increase.

Homeowners can also lower their insurance costs with upgrades to their houses such as stilts and brick elevations that make them less vulnerable to flooding. But the costs, $30,000 in many cases, can be steep.

Baisden said the revision allows primary homeowners to breathe easier, but some critics say their burden should be heavier.

“In general it’s a move in the right direction,” said Eli Lehrer, president the R Street Institute, a conservative Washington think tank, but doesn’t go nearly far enough to fix a program that’s broken.

Discounted insurance is “expensive for taxpayers and encourages people to live in harm’s way,” Lehrer said. “Stupid, rich people who want to should be allowed to build wherever they want to as long as taxpayers don’t have to bail them out.”