The first training session for the Olympic open water competitions in the River Seine has been cancelled, World Aquatics said on Tuesday without initially giving a reason. The Paris Games have been marred by the controversy over the cleanliness of the Seine, with training sessions for last week’s triathlon events routinely cancelled after the water failed pollution tests and one event being postponed by a day. The German open water swimmers led by Tokyo champion Florian Wellbrock had not planned to take part in training in the Seine anyway. The women’s and men’s open water competitions, also c…