Answer: Here's a list of plants suitable for wet areas and most are hardy down to zone 4: http://www.hort.purdue.edu/hort/ext/Pubs/HO/HO_227.pdf
I'm sure you'll glean a few ideas from the list. I wonder if you've considered installing a curtain drain between the stream and the wet area? It can help redirect the excess water. A curtain or French drain is basically a gravel filled trench - or one with a perforated plastic pipe set on the gravel - which can collect the water and disperse it. Might be worth a thought.
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