“We’re on the front line of what is happening with sea-level rise,” Mr. Smyth said. “It has now changed how we live life down here. We haven’t come to grips with where we are and where we’re headed. It’s not an isolated problem — it’s happening more and more.”

Stillwright Point was once an enclave of fishing cottages that later drew commercial pilots craving the island life, just an hour from Miami International Airport. Now, the neighborhood has some million-dollar homes. A single road, North Blackwater Lane, leads in and out of the community.

Residents want Monroe County to elevate their roads and install pumps, similar to what Miami Beach did to mitigate its sunny-day flooding. Rhonda Haag, the county’s sustainability director, said she would ask commissioners next month to expedite road-modeling work, but any actual construction would still be far off. Pilot elevation projects for Twin Lakes and a low-lying community in Big Pine Key that have been in the works for years are planned first.

Elevating a third of the county’s 300 miles of roads could cost $1 billion, Ms. Haag said. “We are the most vulnerable county in the state, if not the nation.”

Last week, Bill Marlow and his wife, Debbie, decided to paddle board across a canal to Jim and Marilyn Anderson’s house for drinks — these are the Keys, after all — rather than expose their car to the elements. The Marlows later hosted a weekend party that involved organizing carpools, identifying paths across yards, and setting up a freshwater station for guests to clean off their boots.

“Being a prisoner in Key Largo is not that bad,” Mr. Marlow, 65, said with a laugh.

Then he measured the water outside his house. On Tuesday , Day 77, it was 10½ inches. “The deepest I’ve seen it,” he said. Nearby, a few wading birds enjoyed a swim down the street.

Neighbors bring groceries to older adults and give them rides so they can leave their homes. They worry that sheriff’s deputies will not want to patrol. Garbage and recycling bins put out for pickup sometimes float away. Restaurants stopped delivering weeks ago. The Postal Service (stopped by neither rain, nor snow, nor high tides, it seems) still comes.