The world's only Key deer, the smallest subspecies of the white-tailed deer, are found in piney and marshy wetlands bordered by the Atlantic Ocean and Gulf of Mexico on the Florida Keys. For years, their biggest threat was being struck by vehicles speeding along US Highway 1 or local roads. But those waters surrounding the islands now pose the biggest long-term risk for this herd of about 800 deer, less than 3 feet tall at the shoulder, as sea rise jeopardizes their sole habitat, per the .

Sea level rise is already altering the landscape of Big Pine Key and at least 20 smaller islands the deer call home. The bulk of the deer live on Big Pine Key, a marshy island 30 miles from Key West. They roam neighborhoods where about 4,500 people live, browsing on lush gardens and drinking water from buckets residents put out for them as natural freshwater supplies dwindle.

Despite strict speed limits and a 2-mile-wide animal crossing under US 1, "some 90 to 120 deer are known to be killed by vehicles each year," says Jan Svejkovsky, chief scientist for Save Our Key Deer. But a larger threat looms. The National Oceanic and Atmospheric Administration projects that by 2100, seas will rise 1.

5 feet to 7 feet in parts of the Florida Keys. The threat is greatest to low lying islands like Big Pine Key, where the highest point is only about 8 feet above sea level. Just six inches of sea rise, expected by 2030, would mean loss of 16% of the freshwater holes on Big Pine Key, says Nova Silvy, a Key.