I would suspect your water temps are low, maybe in the 50s? Your water oxygen is going to be very high, probably near max even without windmill due to wind action and water temps.
I would not see lack of algae as a problem. If you DID have a good bloom going I would worry more about a sudden temp change from a big rain runoff event causing all the algae to die and a big oxygen crash. But with no algae I can't see a worry related to algae.

If water temp in pond is 50 and a rain event happens the rain water is probably air temp or maybe 55-60? Not sure where in Iowa you are. I would think there would not be a big temp difference even with a big run off.

What I"m not certain on, and would like input from others... Is rain water really un-oxygenated? I would think pumping ground water from depth and putting in your pond would add poorly oxygenated water but I have not heard on this forum that rain that falls through the air and then runs over the ground into the pond is without oxygen. anyone?

I know the fish that died in my pond during a huge run off event during a heavy rain probably died from chemicals that ran off the roads into the pond plus the temperature shift. I can't rule out that the stratified water with warm water on top and cooler on bottom didn't also break up and mix with the big surge of new water. It was only my largest fish and the warm intolerant fish that died.