riverwater and seawater has a very different color to normal freshwater (minecraft:water), which gets more pronounced when you lower your brightness from "Bright" to anything below, most pronounced on "Moody". Screenshots of the comparison included (they are taken at "bright", "50%", and "moody"):
vvvv-vvv commented
Also screenshots of saltwater:
Therighthon commented
This has been confirmed to be a sodium issue. We still plan to fix this, just a note for anyone picking this bug up.