The Spirit of Dark and Lonely Water is the symbolic villain of a PSA campaign in the 70s - his role is to personify the dangers of water and reckless behavior by children that often leds to accidents and deaths.
In the context of the PSA he has sentience and seeks to lure all children he comes across to their death - having power over "show offs, fools and unwary" but being powerless against "sensible children".
As a symbolic personification of evil he is similar to Satan and immortal - existing for as long as people do not obey rules around water or endanger themselves.
Throughout the narration he murders children and is in the process of watching his final victim drown when a group of children come to rescue the boy - the demon knows they are "sensible" and is forced to retreat as they succeed in saving the boy but the demon ends by warning the audience that he would be back (as is his nature as an immortal aspect of life).
- The Spirit of Dark and Lonely Water may be an aspect of Crisis, another demonic personification used to educate the public on dangers (though Crisis embodies a vast number of topics while the Spirit of Dark and Lonely Water is much more limited, yet no less malevolent)