There probably aren’t a lot of areas along the shore of the Mystic River that aren’t taken up by gas tanks, smokestacks, and abandoned piers. But River Bar in Assembly Row is located in one of them. It’s an Assembly Row restaurant, so it feels a little Truman Show-esque, but that’s an acceptable trade-off for some decent American bar food that you can enjoy next to fire pits and lighted trees as you gaze out at a somehow green stretch of the river.