A few water birds (like grebes and loons) build platform nests right on the water, where they can float. The nests don't move, though, because they are anchored to plants that are attached to the bottom of the body of water. These birds build nests on water because they don't walk well on land, so they find a shallow (not deep) part of the water to build their nests. Then, they do not "walk" to their nests - they "swim" to it. When the babies are ready, they simply jump into the water and begin their aquatic (water) life.