When I first spotted Le Marcounet it was just one bar boat amongst others that I thought was worth mentioning because of its varied musical programme. In the meantime it has grown to be one of the popular places to go to in summer time, famous for their outdoor concerts and dance parties.
Another fact that has contributed to the popularity of Le Marcounet is the fact that the road along the river bank just behind it has been closed for cars and is now a pedestrian-only area. Logically the river banks are now full of Parisians taking an evening stroll or pick-nick.
I first discovered this bar boat because of the charleston and lindy-hop parties it organizes, but it programmes lots of different live music. If dancing is not your cup of tea, they offer lovely acoustic sessions on Sunday afternoons, too. Just check their programme here. With the setting just alongside the Seine and the large trees on the riverbank, it is hard to find a place more idyllic in central Paris.