Edema while pregnant on vacation despite exercise?

Hi. I'm 20 weeks pregnant and currently on vacation in Africa. I exercise a lot, swim a lot, and my legs aren't swollen during the day. By evening, however, they're so swollen that I have actual dents where my sandals used to be. My feet and ankles are swollen, especially. And that's just from the 1-2 hours I spent sitting at dinner. By the next morning, it's almost gone. Is that normal?