Bosom

It's possible that the extent to which your strength training routine might affect your breasts will surprise you. For instance, increasing the frequency or intensity of your back or chest muscle workouts (the chest muscles are positioned behind the breasts) may have an effect on the size of your band. Because fat loss affects the whole body, including the breasts, it is possible that you may notice a reduction in general body fat as a result of the sort of exercise you are doing. This may result in a smaller amount of breast tissue.*

https://attireproject.com/does-swimming-make-your-breasts-bigger/

Does Swimming Make Your Breasts Bigger?

It seems swimming doesn’t really make your breasts bigger. Like many chest exercises, swimming increases the size of the muscles under your breasts. This, in turn, can possibly make your breasts look bigger, without really increasing their size.

Remember breasts aren’t really muscles, just glandular tissue, and fat. Breast size is moderately heritable and determined by genetic variants. That’s why no matter how often you go swimming, the size of your breasts will be the same.