Hopefully you'll see improvements after it has dried up a little, otherwise I would be watching for signs of fire-blight.
Fruit trees don't like wet feet all the time.

Man I wish I could help you. I still would love a picture :) Good luck.

SCG

Thanks, konrad and SCG. I really hope that it's not fireblight! Yikes.... anyway, here's a photo:

The leaves stay on the tree which looks healthy. I hope it's OK... I have removed all of the mulch around the tree trunk. Hopefully it will dry up faster that way... thanks!

I have absolutely no idea of what I am talking about but if it makes you feel better it doesn't look like fire blight to me.

I lost a newly planted Mountain Ash one particularly wet year and the nurseryman said yes, too wet -they prefer a light, very well drained soil (rocky, or on a slope). Once they are well established, I'm not sure if that's so much an issue unless perhaps it is planted in a consistently wet/compacted spot.

Yeah, I was just going to say probably too wet...not that I know much about them at all, but I just bought a maple this year and on the little planting info sheet it talked about how mountain ash are one of the types of trees that don't like to be wet.

I would third (fourth?) the wet diagnosis. I have a mature mountain ash that does well in my silty, well drained soil, but even then it has some yellowing in wet summers.

Hope it dries out for you and recovers. They're a nice tree.

Thanks everyone! I really hope that it will dry up and get better soon... we shall see. Thanks again!