Psychedelic Trip Out
I have never seen a seagull swim.
Really? I've seen more than enough swimming in the Atlantic ocean when I've gone to visit my family in Florida.
Though, I usually see them in corn/soy fields or grocery/mall parking-lots where I live (central Ohio, tons of ponds/lakes/swamps around for them to swim).
And,
on the rare occasions that I go to them, loads at theme parks(King's Island/Cedar Point/Zoombezie Bay/The Columbus Zoo/The Wilds); but mostly in the parking lots and food courts, where people dump their left over food outside of the cans.
I've heard they are considered pests at landfills (aka trash-dumps).
@OP:
You're an awesome person for even bothering to take it to the vet or care for it at all.
There are tons of people out there who would just shut their patio/balcony door and go about their day; rather than deal with this debilitated "pest" bird.