It is quite difficult to pinpoint these chests' exact location when underwater, the best way to find this one is to look for a huge orange-colored spore/mushroom. You will find the chest in the marked location, as shown in the image below. This underwater location is just behind the large hangar, which is located by the runway. It might be a bit difficult to find it as there's a lot of overgrown weed here. The chest will be next to a huge boulder. This location is directly south of the power plant and solar panel farm. The chest will be in a small open area surrounded by underwater grass or weed. This chest is found in the underwater section between the control tower and the power station. The chest will be next to a rock, as highlighted in the image below. You need to go underwater but in the northern direction. This one is found underwater at the end of the runway. You can find this chest underwater by the north drop zone. There are 9 possible underwater locations. You can find it by the crane at the Main Dock.

This chest location is by El Rubio's western compound barrier or fence wall. This chest is found at the south drop zone. You can find this chest near the air defense system located at the island's very eastern section. You can find this one in the middle of the beach, located east of the central small dock found in the island's middle. This location is at the Northern Drop Zone near the small cabin. You will find some wooden boats by the shore. This chest location is south of the solar panel farm by the beach. This chest location is directly north of the runway in the wide-open area. This chest can be found resting by some water containers at the end of the runway. You will find it at the end of the road that goes around the North Dock. The chest location is in the North Dock area.

Gta v treasure hunt location to bridge