There are several reasons why a sea or river
turns to red. Last month, we reported a lake in France which turned red due to high concentration of salt. Experts say that it is caused by a salt-loving algae called Dunaliella Salina which produces a red pigment that absorbs and uses the energy of sunlight to create more energy.
Another possible reason is red tide which occurs when there’s an algal bloom, an event in which fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water. However, Emily Stanley, a professor of limnology at the University of Wisconsin, said that is it unlikely that red tide is the culprit
When water turns red, the thing a lot of people think of first is red tide. But the algae that causes red tide is a marine group and not a freshwater group, so it’s highly, highly unlikely that this is a red-tide-related phenomenon,” she said.
After ruling out natural phenomenons related to algae, the next possible reason is through pollutant phenomenon. In recent years, due to the industrial developments in its nearby cities, the river has suffered from industrial pollution, agricultural run-off, siltation, and loss of wetland and lakes, which exacerbates seasonal flooding.
“It looks like a pollutant phenomenon. Water bodies that have turned red very fast in the past have happened because people have dumped dyes into them,” Stanley said after ruling out natural phenomenon causes.