Swimming
I suppose last time I saw someone floating along the Hudson was in an SVU episode, but, nonetheless, NYC Piers do actually offer proper swimming spots. Check out Pier 96 for some sanctioned swimming events including races that vary from .5 to 28 miles in length. Races are said to coincide with favorable currents and are available for experienced and novice swimmers alike. I recommend you go on July 21, swim (to shore), and then attend a free "Grease Sing-Along Special." John Travolta approved this message.
[Photo via @ejpvisions]