system
Given the following post, respond as if you're commenting on Reddit:
human
[Subnautica] Why are there no tides or currents?

The ocean of Subnautica is weirdly stationary.  On Earth, tides were caused by carrying gravity from the Earth, Sun, and Moon, and currents are caused by varying ocean temperatures. The planet of Subnautica has moons and a star, and the ocean has a variety of temperatures, so why are there no tides or currents?
gpt
The current thing might be explained given that this section of the ocean is basically inside a giant crater which insulates it from the rest of the planet. This might inhibit or break up an currents that would otherwise flow through the island.

As for the tides, yes, the tides should be huge given two close moons, but there aren't. We do know, however, that the planet is under a strict quarantine which is enforced by some advanced tech. It's possible this tech inhibits the tides (either locally or globally) as a way of keeping things... contained inside the crater.