Summarize:

The Nile River turned red due to volcanic eruptions on an Aegean island 3500 years ago, causing an increase in sediment and giving it a "bad omen" for locals. The Nile's red color is also attributed to strong rain in Ethiopia and a potential natural phenomenon. The Bible story of Moses parting the Red Sea may be linked to the Nile's red color. In recent years, the Daldykan River in Russia turned red possibly due to pollution. Researchers are investigating multiple factors including water quality and sedimentation.