Unlock: Liberate the Bridge Control outpost.
There’s a guy, Steven, outside the poker game on the island west of Bridge Control who’d like you to look into his buddies’ disappearance. The “sacred pool” he mentions is 160 meters north, by the side of the river.
Inside, take a quick swim to find the bodies of the villagers (and, nearby, a Relic). On your way back outside, watch out for a crocodile that’s waiting in ambush. Shoot it, then return to Steven.