Fan Casting Creature from the Black Lagoon

in 1982, a crew goes on an expedition to Central America Nicaragua where local US operatives have discovered signs of a possible lost civilization that sunk beneath the Lagoon five thousand years ago linking to a lost uncharted world of some sort. Said civilization's a time capsule and link to a lost world that's inhabited a race of fish-like humanoids who branched off of humanity, making their home in marine environments across the globe. all the while the crew encounter a mysterious known to the crew as the Gill Man, where they begin to discover some truths and fend off those who dare to find the lagoon for their nefarious deeds.