Irrigation Ditch Question

I live in the Helena , MT area. Last summer a friend and I were
headed out to the Mo. to float in late July or Aug. We were hoping
to do some morining trico fishing. He forgot his hat and as he was
driving we headed back East to his house to get his hat. With the sun
coming from the East we could now see large plumes of trico s
almost like dust whirls over the road. I know they were tricos as
we stopped to get a look at them. The only water nearby was an
irrigation ditch . The water in this ditch comes from the Mo. River
, in the Canyon Ferry Dam, and is pumped thru the mountain to
irrigate fields in the valley. This ditch is dry all winter.

There were millions of tricos in plumes all up and down the road.
My question is do the eggs and nymphs somehow survive the winter
in a dry ditch or are they somehow making their way in the pumped
water from the Mo. Obviously they are mating and laying eggs in the
ditch so the opportunity is there for them to be reproducing
naturally if they can survive a dry winter. If not what a waste of
insects !

MT