I live in zone 7 (MD) and was toying with the idea of leaving
the waterfall running all winter. My brother-in-law has done
so for the last two years with no apparent ill-effects. Whenenver
the pump shuts off, the water drains out of the lines (all run
down hill) so I'm not sure a power outage would have a major
impact and i think my waterfall edges are high enough to keep
water from changing course as ice forms. Is there anything else
to be concerned with? Would that be good or bad for the fish?

Also, when should I dispose of the water lettuce and hyacinths?
They seem to be doing fine right now. Water temp is around 55
degrees and we've had a few very light frosts so far. Thanks!