There are currently somewhere around 800 prisoners floating on the East River, housed inside of the Vernon C. Bain jail barge (named for a warden who died in a car accident). The Department of Corrections uses this to battle overcrowding in the Rikers Island jail complex, and has since 1992 when it built for $161 million. The barge, which was built in New Orleans and brought here, sits approximately one mile west of the SUNY Maritime College (here it is on Google Maps).
Since it is floating and not permanently moored to the shore, "Coast Guard regulations require that she have 3 maritime crew on board at all time, including a mate, an engineer and an oiler."
The inmates on board are medium to maximum security, and are contained within 16 dormitories and 100 cells. There's also a law library, recreation rooms, and a basketball court on the top deck! We've reached out to the Department of Corrections with some more questions about this floating prison, and will update when we have more information.
This wasn't the first of its kind in New York City, either... in 1989 (when there was an influx of arrests), the NY Times reported that locals were outraged when the city proposed "to moor a prison barge on the Greenwich Village waterfront for up to five years." Eventually, "the Army Corps of Engineers denied a permanent mooring application and issued a one-year permit instead" for the 386-inmate barge, called the Bibby Venture. At the time of their report, it was sitting abandoned and waiting to be transported to Pier 40 on the Hudson River. It is currently listed on the DoC's website as being closed, but when it was open it was referred to affectionately by inmates as the Love Boat—one NY Times article painted the scene:
''We live large on the barge,'' declared an inmate, Angel Velazquez, 37 years old, who smiled as he stood on the sunbaked recreation deck watching other prisoners play a loping game of basketball as a sailboat fluttered by on the water below.