From Kenny Unser:
The Rattlesnake is west of Rt. 7 in Falls Village, CT. It is south of Canaan and north of Cornwall. Follow signs to Falls Village. When you see a small cluster of stores, continue under the railroad bridge and around the hydro plant. The Rattlesnake section ends at the Steel Bridge that crosses the river above the hydro plant. The run can be accessed on the river right shore just north of the steel bridge and just below Great Falls.
There is an annual Class-A slalom event on the Rattlesnake that draws boaters from around the country.
Lat/longitude coords are approximate, from TopoZone.
Also check out the
Swift's Bridge and
Bull's Bridge sections of the Housatonic.