Gaia Water is one of multiple runtime modules available in Gaia (Pro) 2023. Its purpose is ocean-style water rendering.
Like any other runtime module, the water can be added to the scene with the "Apply" button from within the runtime module UI. Doing So will add a Gaia Water object to the runtime at the sea level of the scene. The Gaia Water object contains a flat sea plane mesh for rendering a water surface, but also a few additional child objects responsible for underwater VFX:
On the Water Surface object you will find a lot of parameters that will allow you to customize the look and visual effects of the water surface:
Please use the questionmark help button in the top right corner to get additional help on the parameters.
Please note: By default Gaia enables planar Reflections in the built in and HD render pipeline. Planar Reflections are "expensive" performance wise as another camera renders the reflective parts upside down. Consider turning off reflections or reducing the reflection layers / distance to save performance when using the Gaia Water.
The "Underwater Effects" Gameobject has a similar script on it that allows you to configure Visual Effects when the tracked Camera goes below the sea level: