It would be sensible to check it out with the doctor.
I've always had a bit of a tendency to swollen ankles on long trips, also swollen fingers, slightly, if I go on a long walk. I think an element of that is almost natural but recently, in my case, it was associated with high blood pressure, for which I now take meds.
Curiously, I'm having an incredible water whoosh at the minute, and my ankles, which still tend to be a bit puffy at the end of the day, are now bony, like they used to be 20 years ago! It's like I'm losing 20 years' fluid retention all at once!
Can't hurt to get it checked though.