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It's gotta be Dive!
The Beach Houses are probably spots to get Scuba Gear, and the Beaches themselves are probably entrences to Dive Sections, which explains why some of them dont have surfing points
It makes sense since so many of Alolas water types in the dex are based off Deepsea/Seafloor mons like Golisopos, Toxapex, Lanturn, etc.