(Capcom's primary storyline)
Some time after the Annabelle washed ashore in the bayou, the Mold that infested the vessel began to leak out and contaminate the surrounding area and shoreline. Local wildlife soon after came into contact with the Mold, namely, Alligators.
While Joe was bringing back a small dosage of the cure for Zoe to his cabin, several very large mutated Gators lay before him, presumably slain by a rampant Jack Baker as the cabin is engulfed in flames. While Joe was searching for a full dosage of the cure, he encountered more Gators in the flooded swampland.
There is currently a quarantine wall set in place to contain the spread of the Mold. With the Mold outbreak secured within, the Gators continue to thrive.
As the Mold began to fester the swamp ecosystem, alligators soon fell victim to infection. Mutating to abnormal sizes with large teeth that jutted out at unnatural angles, cataract eyes and developing tumorous growths large enough to split open the Gator's tough scale hide.
Gators behaved relatively similar to normal alligators, albeit more vicious. This also changed their attack behaviors, preferring to bite vigorously into prey until death as opposed to drowning them beneath the waters or engaging in a death roll, a signature move of crocodilians.
The only attack they can perform is to bite Joe's torso viciously, causing him to instantly get killed. Gators are extremely weak to spears, one throw can instantly take one down but another one may spawn if Joe stays in water too long so it is recommended to quickly get out of water to avoid an ambush. If he gets out of water, they will despawn but spawn at the same location again (the 1st one in normal difficulty is an exception.) if Joe proceeds to the same water area again. This tactic might be useful for those that are aiming to get the "The Only Guns You Need" achievement since it prevents Joe from using his spears. It is possible to punch an Alligator to death but is very hard to do and not recommended. In VR mode it is possible to punch Alligators while Joe is on land by moving the VR head set towards them which also moves Joe's range of attack without him leaving the safety of a platform or piece of land.