tree dying from wetfeet? help...

I have a tree, actually it was 4 trees planted together to shade the back yard. I am not sure what kind of tree but it has long featherlike leaves and in the summer has a reddish flower all over that looks like a fishing lure. anyway, these trees now 20 ft tall have grown together and formed a cavity in the middle that collects water and debris. this year I am getting no leaves at all except for a couple new branches. also it appears that a couple areas of the bark are splitting amd leaking. I have not been real good about keeping the cavity clean in the past and wasnt truly aware of its depth but now it looks like it is affecting the tree. I have cleaned out as much as I can, as I cannot reach the bottom. I have redirected sprinklers that were hitting the tree. Is there anything else I can do to help save the tree and is there anything I can put in cavity to try to expedite the drying process? Finally what can I put in the cavity if the tree revives to prevent this from reoccurring? thank you

I'm going to guess that it is a mimosa tree (Albizia julibrissin)? http://davesgarden.com/guides/pf/go/1764/ (although I'll admit I have no idea what a fishing lure looks like, so I may be way off!)

Can you post some pictures? That might help understand the problem a bit better and whether it's something that's potentially fixable or not.

wow you are good. that is the tree. here is a pic from google. Do you want current pics of my tree as well? I will try to get some posted later today

How old is the tree? Mimosas are usually short lived and best to remove when dying/dead and plant a new one - they grow super fast. You probably have several seedlings growing nearby.

Yes, I was hoping for pics of your tree so maybe people can see what's wrong with it, how far gone it is, etc.

Ok so we have discovered that it is not wet feet but could just be trunk rot due to a large cavity between 4 trunks. The cavity is approx 30" deep. i have cleaned out the cavity as well as possible and placed a fan in the tree to help dry it out over the weekend. Now I need to know what to put to seal the tree inside the cavity. Can anyone please help?

here is the tree pic

And another view

I wonder if there is anything you can put in the cavity that would seal it permanently. If you did seal it now, you may be sealing in disease and rot. Also as the tree grows the gap between the sealant and the tree would probably separate sooner or later. I know in the past some people used mortar mix or tar but I think those practices are discouraged by arborists.

I'm thinking of the old silver fillings being replaced recently in my molars - eventually they separate from the tooth and allow more decay to occur under the filling. I just hope the new fillings last the rest of my life.

You could drill a hole from the outside at a downward angle to the cavity to allow a drain hole but I don't know if this is any better than what you have now.

Hmmm, I had no idea that the mimosa tree trunk could look so attractive and smooth.

I would probably consult an arborist on this one--if there's a good way to fix this situation they would be in the best position to know what the right thing is to do. Honestly though if that picture is really recent and your tree hasn't leafed out more than what you can see in the one picture, it could be that it's too late--I suspect this has been going on for a number of years and it's possible there's too much rot in there now for it to be able to come back.