Sediment makes the colour
Glacial river Leirá drains sediment-loaded water from Myrdalsjökull glacier. While the fast flowing glacial river appears light brown in colour, it loses more and more sediment in the labyrinth of small lakes and narrow, crooked connections between lakes. This loss of sediment is visible as a gradual change in colour to dark blue.
Eva P. S. Eibl (distributed via imaggeo.egu.eu)