Ordered some expensive new koi and algae eaters- the algae eaters like fast moving water.
My pump has been off since September - it broke and I just got it fixed.
Of course I would love to turn it on, especially with these new fish coming in.
But
Many of my koi were chock full of eggs a couple of weeks ago.
Since then, the "fat" ones have gone into hiding.
Only males are coming to the surface for food.
I'm thinking that they are down at the bottom with eggs, and this is so exciting to me since I have never had koi old enough to spawn!

If I turned the pump on, it would pull from the bottom drains and ... get the eggs?
What do you guys think?

If your fish have not yet spawned, you could hang spawning mops into the pond for the females to deposit the roe onto.

The mops can be made from hanks of wool cut and tied at one end to form a mop or from nylon rope that is cut about a foot long and teased out, tied in bunches and hung into the pond. The roe will stick to the spawning mops better than to the sides of the pond. The wool or rope mops are also safer for the fish, as they are soft and will not damage the females body during the throes of spawning.

Other fish will feed on the roe that sticks to the mops but there will be plenty left that survive. You can also remove the mops and place them in another pond or container that does not have other fish in it, if you really want lots and lots of Koi or Goldfish fry.

For people that do not want additional fish in their ponds, you can remove the mops after the fish have spawned onto them and dip them into a pot of boiling water for a second or two. That will sterilize the roe and the mop can be put back into the pond for the fish to feed on the cooked roe.
"Horton"

I'm not new to koi, but I am new to "hiding" koi.
Do you think it's feasible that the reason they are hiding is that they are fanning eggs, or whatever they do after spawning?

When fish spawn it is a busy time for them in the pond, with the males relentlessly chasing and nudging the females to release the roe so they can fertilize it.
If your fish are sitting on the bottom they are not spawning or "fanning". Once the females spawn the roe is on it's own to develop, there is no after care or babysitting.

You will know when the time comes, as the pond becomes a frantic scene of "flashing" fish. Koi usually spawn when the water temperature is around 68F.

"Horton"

I do not believe that the male Koi are any braver than the females, maybe just hungrier, so it is difficult to say what is/has been going on. They could have had a scare.
How has your weather and temperatures been of late?
If the temperature has been on the cool side, that could have a bearing on the female fishes behaviour.
If they are full of roe and ready to spawn and the water is still too cold, they will wait until the temperature is right for the games to begin.
"Horton"

Has there been a predator? Well, my pond edges drop sharply to 4', and is 5' in the center, so I don't see any racoons getting in there. I've got 4 dogs and 2 cats that sleep within feet of the pond, so I can't even imagine a crane or heron staying for long. But I do live near a huge lake and right next door to a cattle pond and a stocked catfish pond, so those birds fly by a bit. There are lots of trees and cover for the fish so maybe we haven't been noticed yet.

I have a turtle predator, but he's been here since last year and they just started hiding 2 weeks ago. He definately IS a predator, as I found a half a fish in my pond last fall, and 2 different halves this spring thus far. I am trying to get rid of him.

I had a snake predator (see below) but he's gone now.
Actually, the fish started hiding right AFTER snake was out of the picture.

As for spawning, my goldfish are VIOLENTLY spawning as of this morning. But the koi are still hiding. All except for a couple of males.

Thanks for your help, guys.