I tend to agree. I usually claim that I can't swim, as what I do doesn't really constitute swimming, but I can stay afloat and move in a deliberate direction.
A complicating factor: Swells and bad weather make it a lot harder. But on the flipside, no matter how badly it goes, if I'm teleported back in 30s I'd just fill my lungs beforehand. I can hold my breath for much longer than that, and even if I couldn't, it would take more than 30s to die from oxygen deprivation - just make sure I have EMTs on standby for when I return.
Surface of the ocean or anywhere from the deepest trench up?
Surface, no brainer, I can swim for 30s. Below the surface, you'll be like the surfaced blob fish before the end of the first month.
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