The Mianus River begins as a small stream. As it travels south it widens and pools above a dam in Old Greenwich, CT in a wooded residential area. It is ideal for paddling under time constraints, as it is very quiet, easy to get to, and small enough to cover in under an hour. It's a great spot to practice skills because of the absence of boat traffic.
The river itself is very deep in the middle (I've heard 80ft from Greenwich residents) and is a source of Greenwich's drinking water. It's exceptionally clean. There ARE weeds, but only in the shallow areas.
There's a small bridge upriver. Passing under it will bring you into a surreal spot. Lots of wildlife and it looks untouched by human hands.
N.B. When the river is flooded, i.e. after heavy rain, I've heard that the dam is dangerous. Be careful of drifting off the dam with excess water.
There is room for 4-5 cars. There are no facilities or picnic tables. The path to the river is very steep - be careful of your footing. The land surrounding the river, with the exception of the launch, is all private.
I-95 to exit 5. Turn left on Route 1. Pass Hay Day Market, Citibank, and go over a small bridge (you can see the river dam on your right). Make a right on River Road immediately following the bridge. At the end of River Rd, make a right onto Valley Road. Follow for a brief distance to a dirt pull off on the right hand side of the road.