In case you need a refresher on where Gigi and Bella Hadid get their model figures from, let this photo of their mom, Yolanda, serve as your refresher.

The former Dutch model was up for a sunrise swim in Lake Constance -- which borders Germany, Switzerland, and Austria -- and flaunted the incredible view. Double entendre fully intended.

Yolanda -- who is 53, by the way -- has famously battled Lyme disease, and says the ice cold morning swim helps with inflammation.

We're no doctors, but if it's working for her ... it's working for us.