The marsh deer (Blastocerus dichotomus), sometimes known as the swamp deer (not to be confused with the barasingha of India, which is also known as the "swamp deer"), is a species of deer native to South America. It is the largest living species of South American deer. This is the only species in the genus Blastocerus.
In 1987, the Tucker family had moved from Burlington, Vermont to a lodge located in the swamps of Florida, dubbed the "Fever Swamp", to start a scientific experiment. They had bought and imported a herd of marsh deer from South America into their temporary holding pen near the Tuckers' lodge, to determine if marsh deer could survive in Florida's environment, aiming to introduce the species to act as ecological proxies for the highly-endangered Key deer (Odocoileus virginianus clavium), which had disappeared in much of its range.
There was a brief incident, where one of the captive marsh deer in the holding pen was attacked and killed by a yet-to-be-determined carnivorous mammal, possibly by a Florida panther, an American black bear, or a feral dog. There was a rumor that a real life werewolf had attacked the marsh deer; however, this is not without scrutiny, and is extremely unlikely due to werewolves being folkloric creatures rather than real organisms.
The marsh deer, due to having adapted to their new surroundings, have thrived in the Florida state, having filled a niche similar to whitetail deer, and have continued to do so even today. However, some conservationists and farmers have expressed concerns, with the conservationists fearing that the nonnative marsh deer might outcompete local whitetail deer populations native to Florida, and the farmers worrying that marsh deer could eat their crops. As such, the marsh deer is regulated by legal hunting in some areas, and the marsh deer are tracked with the collars to help scientists and conservationists know if the marsh deer are causing issues or not.