The water is an aphrodisiac

For a while it all seemed normal as the subjects slowly swam around the shallow ocean. The drones and cameras didn’t immediately pick any strange reading that might indicate danger from the water, or anything else in the environment, for that matter.

However, after some time, all 6 subjects began to act strangely. While before they were swimming randomly and enjoying themselves in the water, now the all seemed to be converging near the shore and were no longer doing anything other than swimming and looking at each other.

Through the drone cameras, the Captain recognized the look in their face. Lust, pure lust towards one another. They quickly come together and begin foreplay, with some groping, kissing and more, as they get more adventurous. To the Captain it was immediately obvious that the water had something to do with this, and that this ocean was a powerful aphrodisiac.

Quickly ordering for samples of the water to be collected, the Captain got back to observing the subjects, who were now on the beach and actively having frantic sexual activity. Despite the strangeness of it all, the Captain decided to allow it and not send anyone to intervene, out of both fear for the safety of anyone who tried to stop them and scientific interest in what would occur afterwards. A note the Captain felt worth noting was that it was all heterosexual sex, which seemed odd. A true aphrodisiac should also lead to some homosexual sex too...

This was when a theory was formulated that whatever caused that reaction sent their reproduction instinct into overdrive, which would also explain why only vaginal sex was occurring between the subjects. The cameras recorder everything, from the moment they entered the water to when the last duo finished having sex, all of them having cum inside. Afterwards, the subjects all passed out after a short while, just enough time for them to come apart, stand up and look at each other with confused faces before they collapsed on the sand.

Once this happened, the Captain had them recovered and sent to the lab for a further look at possible side-effects the water may have had on them, and issued an order to avoid any naked contact with the ocean until the lab yielded results on the cause of this orgy and the safety of this water for humans, given what it had done to the subjects.

While the lab worked on the water and the subjects, the Captain began to plan the next experiment, including the possible use of scuba gear and their submarine to explore what the underwater world had to offer them in terms of wildlife, resources and new discoveries. Or maybe they could turn their eyes inland, to the strange and alluring rainforest that began where the beach ended, and had potential for mystery and discovery.