The bark will look as well as feel rotted and loose. It sounds like you might have still planted the right trees for a location like that. I can verify because I live where the Mississippi River is and see this flooding every year. Worse cases than your's actually. Hopefully you planted Red maple or another such as, ...Silver.

If for some odd reason you do have problems, you'll be 100% better off to plant small bare-rooted seedlings during early spring just before the buds break and when the soil is workable. For me, zone 5 Illinois, I figure on mid-march as being the best for me. I typically from reading have learned an estimated time of two-weeks being the seperator of such. A zone above mine, I apply two weeks to earlier a beginning of Spring as well as a two weeks of "hardening off" during fall. Same goes for colder zones, oppisitely, speaking.

A list of trees that tolerate water and information supplied by Co-author Guy Sternberg who's a friend:

Taxodium distichum, Nyssa aquatica, Salix, Carya aquatica, Forestiera acuminata, Planera aquatica, Nyssa ogeche, Itea virginica, Quercus lyrata, Larix species, Sycamore.

"I think the edge is your safest bet. If you go deeper, try to use small bare root plants that have not been grown in a container or in upland soil in a nursery for very long." Guy Sternberg

More information supplied by GW member: Resin

"You can plant direct into the soil at the bottom of the pond, as long as it is not more than 50-60cm deep water." Resin

Dax

Thanks for the info Dax. My real problem is that these trees are mature, tall (approximately 40+ feet in height) and I am worried about them rotting, splitting apart and falling. So far there are no outright signs of splitting. I would like to save the trees if possible. I am hoping to come up with ways to clean out the valleys in the tree trunks and fill them with some sort of material that will prevent a rainwater build-up, if it isn't too late.

OP wrote "I am hoping to come up with ways to clean out the valleys in the tree trunks and fill them with some sort of material that will prevent a rainwater build-up, if it isn't too late."

Leave them be. As long as the water is in place, the trees won't rot.

"Cleaning" out the area will help problems spread further than they may already be.

I dug out a bunch of black sludge from in between the valleys where the main trunks meet on each tree. I looks like the water has rotted the tree trunks to at least a depth of 12-15 inches from where the trunks meet. On each tree, the trunks meet about 6-7 feet from the ground. In each case, the two trunks that meet and form a "y" are each about 16-24 inches in diameter. The pools of water gathered in the valleys between the trunks are about 6-8 inches wide. I'm not sure how far down the rotting goes into the valleys. Would this not continue to rot the trees if I don't do something about it?

Billy

As said, the water-filled holes in trees don't increase rot.

But from what you describe, the tree could split with the least provocation. If nearby targets are structures or people, it's considered a hazard tree. A very bad thing.

Suggest you have a certified arborist or two for an on-site evaluation.

To locate a certified arborist, look in the Yellow Pages under the heading of Trees, Tree Care, or something similar.