Never, ever, let small children or pets play in lagoons or on the banks of lagoons. Alligators are so fast a pet can vanish before it's owner can take a deep breath. If you catch a fish in a lagoon and an alligator wants it, give it up. Reeling in the fish close to you is a very bad idea, as the alligator will see you as competition for food. If someone tells you there are no alligators in a given lagoon all they have done is display their ignorance about alligators.
Alligators move around and frequently relocate.
There have been very rare instances of alligators at the beach. Alligators can stand salt water but prefer fresh or brackish, so an alligator at the beach is out of it's normal environment and probably lost. Just keep away from it - if possible report it. They breath air, are warm-blooded, bear live young, and suckle their young. Mothers take care of their young during their first year.