Aquatic life disappeared 3 days ago from my Roku 3. The Premier+ in the bedroom still has it so know it is still available. I've updated the software and not even available as an option in screensavers.
Not sure if because Roku 3 is old. Anyone else with a Roku 3 having same issue. Loved having the screensave as it is relaxing. The only other option is to have to purchase one.
There are two versions of the Roku 3: the 4200 (Mar 2013) and 4230 (Apr 2015), so depending on the version yours is either 9 or 11 years old. While both are still officially supported, it's certainly possible the player simply can't handle the demands of that screensaver. The user interface only supports 1280X720 resolution, and that might simply not be enough for that screensaver.
I wouldn't be surprised if Roku finally moves both of those models to the legacy list and drop support. It has to be more work to still maintain the OS for that old of hardware.
Try performing a Search for "aquatic" or "aquatic life" from your Roku Home Screen and see if it is available as a channel/app install instead of a screensaver for your Roku 3.
On some RokuTVs and devices you first have to install it as a channel/app and then you will find it under your Settings/Themes/Screensavers as well as located amongst your channels/apps on the Home Screen. (means you can also launch it whenever you want from the Home Screen).
On other Roku devices, it is simply a screensaver. (no seperate channel/app install required).