this is the river at dusk, when the water looks pink and a mist rises from it. I've heard that this is a time when supai, spirits* are about, and when children are not to play by the river for fear of their being taken away or falling into the river, though they are perfectly allowed to play in the water at other times of day.
*this is not an accurate translation, as such concepts almost always come with their own lore and connotations and superstitions. Supai is often translated as demon or devil but they are much more ambiguous in nature and a little more flesh-and-blood too. I'll try to find something more on this to post because it's one of the most fascinating aspects of Runa culture, to me.