Strange sky phenomenon - a weird smoke ring above Lake Zurich baffles residents and scientists

S.O.T.T: What is this smoke circle above the lake of Zurich? A Big Pothead? A new type of UFO? A heat phenomenon? Someone smoking a large joint? American Indians making smoke signals? A mirage? A volcanic eruption (but no volcanoes around)?

Although this event remains a mystery even for scientists, lots of people were amazed in front of this odd sky phenomenon. What do you think? Have you ever seen such a smoke signal before? Do you have any idea what it could be? ... read more>>>...