all willows will thrive in that condition. corkscrew will is a cool plant you may want to check out. bald cypres, black spruce and eastern larch will do well also

Not sure about eastern larch in heavy clay...they are usually in boggy high organic soils. Swamp alder might be a good choice, they have very nice male and female catkins, and can take wet heavy soils. Where I grew up, the woods behind our house was swampy (standing water most of the year)and Pin oaks did wonderfully under those conditions, so that may be an option as well and are easy to find!

thanks for the suggestions. Are all these hardy in Zone 4?
How about scotch pine?

a definite NO on the Scotch pine. Hates wet feet. I'm not certain if bald cypress is zone 4 hardy, ask your extension agent or local plantsman. the others all are hardy in your zone as is eastern arborvitae or white cedar Thuja occidentalis. Saw it growing is swampy areas in upstate NY.

Seeing that I live in Florida and see alot of magnificant bald cypress trees, I decided to do a little search on them for you. I found the following web page that gives the hardiness zone for bald cypress.

Enjoy,
Scott

Here is a link that might be useful: Bald Cypress

Den, without knowing the size of your yard, its hard to recommend. Turn to nature and see what grows naturally under wet soil conditions.

Unfortunately, many trees adapted to wet areas have some undesirable characteristics. Rapid growth leading to weak wood, messy habits, surface roots that interfere with lawns, and short lives. Willows and silver maples fit here.

Here are a few with more desireable traits:
Red maple. Likes acid soil.
Ash trees. Both green and white.
Kentucky coffeetree. Unusual and pest free
Swamp white Oak. Oaks are the 'royalty' of trees.

Smaller trees: alder, river birch and serviceberry

These few evergreens: White spruce, arborvitae, hemlock and tamarack.

These shrubs: Redosier dogwood, viburnum, chokeberry and silver creeping willow.

I have most of the above in my back yard which is barely a foot above the water table. I hauled in many yards of soil to make raised beds nearly seven yrs ago. Plant everything as high as you can. Water logged soil kills all oxygen, which is necessary for the life of any tree.
Pondy

How will Arborvitaes do in wet areas? I am in the Lake George area of upstate New York. Looking for something fast-growing, that will get tall, preferably an evergreen--I know I am being picky, but would like to screen the property/house next door.

Thank you for your advice.....