The only dam that was directly built on the Columbia for power and water for irrigation(Banks Lake) is the Grand Coulee Dam. The others were built for power production and since they backed up the river then people took advantage of the lakes created and started putting pumps on them thus opened up more land for farming.

Also on the lower Columbia they saw that with the lakes they could use barges thus they built passages for them.

I agree we need to find better sources for power. But coming from the Okanogan I know the people of the Basin wouldnt have water if it was not for Banks Lake( the Columbia Basin is the only real receiptient of the irrigating purposes of the lake).

As for power hurting the fish in the dams. That is not a real issue as it is sent out quickly form them the danger comes from the power lines crossing the river it has similar effects on fish as it does in humans if the fish stay under them for long periods but as we know fish move so in reality it isn't a real concern.

Just my observations from growing up where the dams are more important.