FLORIDA KEYS (CBSMiami) – There are troubled waters on the horizon for the Florida Keys. Monroe County made a shocking announcement Wednesday that some roads and homes may be surrendered to the sea. It’s all because of sea level rise.

The county could let roads sink below the surface, cutting off homes or even neighborhoods.

The revelation comes from a study to raise some 300 miles of roadway indicated it would come at a very high cost.

After seeing the estimate, more than a billion dollars, county leaders said for some neighborhoods it just might not make economic sense to save them. The county is discussing alternatives like replacing roads with boats as well as raising taxes to pay for the roads that are raised.

The 51-page report on climate change in Monroe County is alarming. It noted this year’s seasonal tides are setting records. It also indicated sea level rise projections increasing. There is a chart of the most vulnerable counties in the United States, and Monroe County is now holding the undesirable honor of number three in the country. They hold first place in Florida.

County Sustainability Director Rhonda Hagg said they face a much more difficult situation than Miami-Dade or Broward County.

“We are surrounded by water. We have hundreds and hundreds of shoreline, and it’s comes in from all sides. You cannot build a seawalls around the islands. No. 1, it would be way too cost prohibitive and it wouldn’t necessarily work,” Hagg said.

The county is half way through a study to save the Keys’ 300-plus miles of roads. These are roads that lead to homes, businesses and the mainland. Many are projected to completely disappear below the surface in just 20 years.

Areas like the bayside of Key Largo, Sugarloaf Keys and Big Pine Key all appear to be at greatest risk.

Preliminary budgets indicate the price tag to raise roads, install drains and pumps could be a billion, possibly even billions of dollars.

County Administrator Roman Gastesi believes the solution is not going to be easy. Some property owners are likely going to lose their homes.

“The Keys are not going to save everybody. Your Keys are not going to look like they are today,” Gastesi said.

He believes most homeowners, once they see the numbers, will agree that is more cost effective to move than to try to build the area up.

Gastesi told CBS4 he could see the project funded by increasing sales tax – a resiliency tax.

“Right now we are at 7.5 percent sales tax in the Keys. I’ve traveled in some areas that are up to 10 percent,” he said.

Gastesi suggests the county could raise rates to 8.5 percent to cover the cost of the project. In general, roughly 60 percent of sales tax in Monroe is paid by tourists.

Residents would have the opportunity to vote on it.

But even if they find the money, it’s apparent some roads and homes may not be saved.

Gastesi explained, “It doesn’t mean that we are going to spend $20 million dollars to go down a small road to get to two or three houses. It just doesn’t make sense. We may be better off buying those two or three houses or letting them know that we are not going to provide them services.”

While the county administrator is sending out a warning that residents may need to move or use boats to get home, there is still hope for resolution.

Hagg told CBS4 she sees innovation and partnerships drive costs down. If private industry gets involved, the price tag may drop.

“It’s not all doom and gloom here. There is a lot of high hope here,” she said.

While optimism is high, the county has already hired lawyers for advice. They are asking questions like “Do they legally have to raise your roadway?” and “Can government plan to let a neighborhood go underwater?”

Previous court rulings send mixed signals.

As for a timeline, there is still a long way to go. The study is expected to wrap up in late 2020. Decisions on what roads to save will then be debated. One can assume lawsuits from homeowners may be filed as well as.

Assuming the county finds funding to do all this, the soonest the Keys would see construction to raise roads is likely 2023 – barring no legal fights.