This Saturday is the official International Beach Cleanup Day Sept 17th.
If interested ,  check out this information From the NY Harbors Parks website:
9/17, call the American Littoral Society, (718) 474-2643, for times & locations
International Beach Clean-Up 
Help clean the shoreline of Jamaica Bay or the beaches of Rockaway. Groups are welcome. Bring work gloves, sun/insect protection. Wear waterproof boots or old sneakers. 
or
go to  http://www.alsnyc.org/ and click on the crab icon  "Beach Cleanup"