Eight of us had been swimming at Dores and noticed the ISS crossing the evening sky when a white sphere about the same size as the ISS moved from the north west quite quickly towards it to the extent that we commented on a possible collision.We noticed that the object was moving backwards and forwards, sometimes quickly, sometimes slowly but generally not in a straight line and was a slightly paler light than the ISS. After pausing by the ISS it then moved fairly quickly but on an erratic path towards the west but on the south side of Loch Ness. We commented on the fact that none of us were aware of planes or similar that could fly in this way.