A picnic on the Seine is a great way to wind down a day, but a rooftop bar on the Seine may be even better. Here are our top three choices for the best boat bars on the Seine (in the Port des Invalides/Quai d’Orsay area) that you must check out this summer before they float away from the 7th arrondissement and your rosé préférée is gone to be replaced by mulled wine. 1) Rosa Bonheur Sur Seine: an offshoot founded by the team behind the Rosa Bonheur situated in the Parc Buttes-Chaumont, this immensely popular floating barge bar is packed to the brims with people. While it seems like the sides of the boat are bursting with action, it’s actually the dancefloor inside that has all the main attractions. With an eclectic lineup of music going from hip hop to blaring wedding music in one swoop (don’t be…