Indignation, after river blocked - no power now? (6)
I believe the answer is:
outage
'no power now?' is the definition.
(period with no power)
I can't explain the rest of the clue.
(Other definitions for outage that I've seen before include "Temporary suspension of operation" , "loss of power" , "Emaciated" , "Gap in power supply" , "time of no power" .)