It reminds a bit of the Brazilian rain forest - at the famous location where the dark waters of Rio Negro river meets the bright waters of Amazonas. But it is a landscape in Southern Germany, a floodplain forest at the northern rim of the Alps, called Pupplinger Au - very small, totally only 7 kilometres long and 2 kilometres wide. There the rivers Loisach (dark water) and Isar (bright water) meet. After heavy rainfalls in the Alps the water rises in the river beds. They change from very calm to wild and turbid - and they get intensive colours.
Where does the intensive colours come from? Heavy rainfalls wash a lot of soil, sand and loose stone into the rivers and make them murky. Calcarous rock particles and a bed of light-coloured gravel make the Isar water milky and bright. The river Loisach flows through a huge marsh where it absorbes a lot of soil and humic acids before it reaches the floodplain forest. This makes it dark brown and muddy.
The different loads cause different concentrations. So the waters cannot mix at once at the confluence. For some hundred metres the two river waters flow side by side in one bed creating spectacular swirls.