This effect cannot be detected by Arbitrary Mipmap Detection normally, as the sand is just a standard mipmap, so at higher internal resolutions the ocean will appear a bit greener. Super Mario Sunshine reads the mip level of the sand to change the color of the water slightly in the distance.
To solve the problem, simply disable the code. This has been confirmed with a 'Press B to run fast' code. If certain Action Replay codes are activated, then the game may crash upon trying to return to a completed level. $Instant Scrubbing Sirena Beach Completion As a last resort, consider using the Gecko code The nature of the level can make it hard to know whether the bug or an incomplete cleanup is responsible for failure. For example, user VinDuv reported switching from DirectX 12 to OpenGL solved the issue in 5.0-1331. There are various solutions involving changing graphics settings.
This bug was at one point regarded as fixed and present only in old versions (3.0, 4.0), but it is still commonly reported and can still be a problem under certain conditions. There is a bug in the level involving a timed cleanup of Sirena Beach where a complete cleanup would go undetected.