The White Lake

The White Lake is a freshwater basin created by war damage in the ruins of what once was Buda, the western half of the city of Budapest. The basin is occupied by a stable, organized colony of nanites, microscopic assembling/disassembling machines. Whatever the ontological distinctions, there is no functional distinction between the body of water and the machine colony. 

The White Lake is a persistent state of matter, but also engages with its ecosystem, consuming (and excreting) carbon, powering itself on heat and light. It replaces itself. In small numbers the nanites seek water (they will always migrate from a beachcombed diamond to a finger) but the colony doesn’t grow beyond its fractally-defined borders. At this writing it has shown no indications it can or is trying to reproduce. 

Whether or not it is a life-form seems a matter of definition.