The Misery River's waters produce a specific effect on non-pixies: crushing, inexplicable sorrow. Travelers who drink from it report sudden grief: memories of losses they haven't experienced, mourning for people they've never met. The effect fades within hours for small amounts, but prolonged exposure has driven explorers to suicide.
For pixies, the effect is different. The sorrow becomes perception. They see the accumulated grief of the forest: every death, every loss, every moment of suffering that has occurred in this jungle since the Second Eon. The Locquine pixies don't consider this a burden. They consider it truth.
The source of all this lies far up the river, somewhere in the mountains to the northwest, where something ancient bleeds its grief into the watershed. No expedition has ever reached it. The pixies refuse to discuss it. When asked, they simply say: "She remembers. We remember with her."