@Kristina542
Well that's super annoying.
I think that @Fred13 is right that guests don't pay too much attention to the rating unless it's very low. I think most guests view any rating 4.5* and above as really good as that's how it is in most review sites. Judging by your other reviews, this one will soon be buried under other glowing ones and your rating will go back up, although the latter may take more time.
However, if the 3* really bothers you (and it would bother me) or you are aiming for Superhost status, then you could consider asking the guest to remove the review. ONLY do this if you feel like the guest is a super nice and reasonable person. Probably, they didn't understand that 3* is very low and is going to hurt a host because that's not how Airbnb puts it to them. Airbnb tells them that 3* = good.
I did this once when a guest who seemed very happy with her stay left me 3*. I had an inkling why this was (she had asked for an extra discount before booking and I had said no). So, I messaged her asking her what she was unhappy with during her stay and if she could give me some feedback. She was surprised as she didn't realise 3* was low and would cost me my Superhost status so she agreed to have the review removed.
Note, I did not initially ask her to do this, I only asked for feedback. When she said she would change the rating, I explained that wasn't possible, but she could have it removed, and she agreed.
So, although your guest mentioned the shallow dock, you could still ask for feedback, and word it something like:
"Hello X, thank you so much for your review. I was a bit surprised though that you left 3* overall when you said you had an amazing stay. That's a very low rating on Airbnb (a listing can get suspended or delisted for those kinds of scores) and all my other guests have left 5*. So, it would be really great if you could please provide me with some feedback if you were unhappy about anything. I trust it was not the dock, as that was something already mentioned on the listing? Please let me know if there was anything we could have done better. Many thanks, Kristina."
Or, you could just let it go. Sometimes guests respond well to this and sometimes they don't... You need to make a judgement call based on your experience with the guest.