Anyone standing on the Pointe de La Jonction Bridge in the Swiss city of Geneva can witness a spectacular natural phenomenon.
Two rivers, the Arve and the Rhone, flow into one another.
What is special about it is that the water here has different colors over a short stretch.
Here the Arve flows into the Rhone and as this happens the water has different colours.
But what exactly is behind it?
"The Rhone flows out of Lake Geneva and therefore has clear, slightly greenish lake water." Martin Pusch from the Leibniz Institute for Freshwater Ecology and Inland Fisheries; "Its water is very clean because it only carries a few floating algae from the lake." The water of the Arve, on the other hand, is cloudy because, as a typical mountain river, it takes numerous suspended minerals with it on its journey to Geneva. Especially when there is snowmelt or rain in their catchment area, which stretches towards Mont Blanc. This is rock that is slowly ground down by the water until finally only fine sand is left. This is whirled up and then colors the water of the Swiss stone pine brown.
"When the two rivers meet, they don't mix immediately," says Pusch. "Rather, there is a sharp dividing line between the two bodies of water, which is also due to the fact that the two rivers flow at different speeds." The main reason, however, is the movement of the water itself. "It never just flows straight, but rather in eddies and spirals. These are usually invisible. But because the two rivers with different water colors unite here in Geneva, these turbulences become visible."
