Rectangular Body Shape, have a straight body line. Create a faux waistline with the swimwear silhouette.
1. Wear swimwear that have a predefined waist line.
2. Invest in swimwear that highlight the balanced upper body and lower body, and give an illusion of a waist curve
3. Belted, curved or illusion swimwear works very well for this shape.
Read here for Kaftans for Swimwear.