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"