This sign was especially enigmatic.  Exactly what type of activity are they attempting to...

This sign was especially enigmatic. Exactly what type of activity are they attempting to discourage? Dynamite fishing? The message seems so awkwardly worded that I feel like I may have missed the point of this sign entirely. Again, I didn't see any power lines going anywhere. Best I could tell from researching later on the Internet, these reservoirs are connected to the Los Angeles Aquaduct so presumably some of Los Angeles' drinking water comes from here.

Location
YosemiteAnsel Adams Wilderness
Photographer
John Hovell
Date taken