I hope this is self-explanatory, but when I sprint or swim in the water (Ctrl + W) in Creative Mode, with at least one dolphin within pretty good proximity of me, the dolphins don't follow me around nor simultaneously grant me with the "Dolphin's Grace" effect. Therefore, it is impossible to swim with Dolphin's Grace in Creative Mode unless you use /effect command.
This has been since a certain 1.14 release, not sure which one.
Thank you for your report!
We're actually already tracking this issue in MC-148635, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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