There’s a fair few mods about which add water runways with parking/mooring spots like Misty Moorings posted above. Made a thread about them a few months back here: (Sorry Xbox users, hope you can get freeware mods one day!)
That one seems to come from a bush trip, LNM says ‘microsoft-bushtrip-sanjuan\Scenery\bushtrip-sanjuan\Scenery\San Juan.bgl’ so whoever made that bushtrip added in the parking spot. Very rare that happens in my experience with the first party stuff.