Sanzu River
The Nighlok Monsters are Yōkai-like monsters used by the villains to attack the Human World. They are dependent on waters from the Sanzu River for survival, therefore needing the negative emotions of humans to keep it from drying out. They are trying to expand the Sanzu River to make it flood into the human world so the Nighlok can rule both worlds. All Nighloks have an ability to enter the living world through cracks and narrow gaps. When a Nighlok is destroyed once, it can grow into a giant Mega-Monster on its own that the Rangers need to use the Megazord to defeat. When a Nighlok is destroyed, it ends up in the Nighlok Heaven as seen in "Party Monsters."