If you pump the water out of the holes, just before you pour, you should be in good shape. For a barrier, you could build a form (Assuming your just digging a footing and pouring concrete directly into the hole).
The concrete will have sufficient time to cure. It will be hard enough that water will not effect its strength. When the water does come back, it will be there to stay for the most part. It will act almost like flooding does for a slab, a consistent amount of water over cured concrete will only make curing time longer, and when you cure concrete for as long as possible you can achieve impressive strength.
If you don't pump the water out of the holes, and pour over that. You could be in some trouble.
We did a pour for concrete piers 10 feet deep, about 5 feet was under water, for whatever reason we were told not to pump the water out of the form, and poured it. The water rose with the concrete all the way to the top of the form, we had to take a shovel and scoop all the water off the forms, before we could float it off.
The pier came out pretty bad, there wasn't bad honeycombing, but dusting occurred, and the surface looked like somebody took a jackhammer to it, and just went banana's.
-Bill
