The runoff of nitrates is poisoning the lake.

HSINGKUO county in the hilly region of southern Kiangsi province was one of China’s earliest revolutionary bases.[…] Surrounded by mountains and crossed by the Lienchiang River, Hsingkuo county lies in a beautiful natural setting.]

... A horse labouring under a temporary injury, capable of being speedily cured, is not unsound within the meaning of a warranty of soundness ...

The presence of nodes in multiple layers of a system is the key to understand emergent phenomena, adding an extra dimension explaining what is the role not only of the intralayer interactions, as in a monoplex framework, but also of interlayer interactions for the emergence of these phenomena.