Because of the way the kidneys interact with the body and handle the process of urination, they also are largely responsible for removing the extra fluid within your body.
Kidneys that are starting to fail won't get rid of that fluid as well as they should. As a result, it stays inside the body -- and while it's in the body, it has to go somewhere; the fluid starts filling in pocketed areas.
You may experience swelling in one or both ankles, the legs, the face, hands, as well as feet. While the swelling can be mild, it can also swell to difficult stages; for instance, it might be hard to wear a regular shoe.