I was swimming in lake zug, close to a public bathing area ("badi walchwil"), swimming on the back, eyes up. wheater excellent, blue sky. all of a sudden i observe a white object. at first, i took for a plane in the sky, but it moves much to fast for that. then i realize that it is much closer. actually very close. it moves slowly at about 20 degree ancle towards the water surface in direction of the "badi", from which i am only about 40 meters away. first, i take it for a drone. but it makes no noise, is round, about size of a small egg and has no rotors. it stops about 7 - 10 meters above the surface between me and the shore. then it starts moving again and continues with ascending ankle over the badi towards the adjacent mountain until it is out of sight.