"Folklore: rivers often demand regular human sacrifices in exchange for the fertility they give; river-spirits are often mermaids who demand salt thrown into the water, sacrifices, incantations, etc. to counteract the human sacrifice; this knowledge often cause the refusal to help a drowning person" De Vries, Arthur. Elsevier's Dictionary of Symbols and Imagery. Bingley: Emerald, 2009. Print.
I must have dreamt this three years ago; it surprises me that I didn't find this interpretation sooner. Chilling how spot on the imagery and the folklore explanation is. It's common for me to relate to the folklore entries in the Elsevier's book. Not sure if it's personal preference or my unconscious is tapped into that particular collective well. Whatever the case, I always find something profound in this book. Highly recommended for the serious dreamer.