OARS, the watershed protection and preservation organization, will hold its 31st annual river cleanup Saturday, Sept. 16 from 9 am to noon. Volunteers will walk along the banks or wade into the Assabet, Sudbury, and Concord rivers and tributaries to clean up and help restore the rivers. Trash, tires, bottles, car parts, bicycles, and more will be collected for appropriate disposal. This year, the cleanup focus will be in Westborough, Northborough, Framingham, Wayland, Sudbury, Marlborough, Hudson, Stow, Maynard, Acton, Concord, and Billerica. To volunteer, call 978-369-3956, e-mail firstname.lastname@example.org or visit www.oars3rivers.org.Jennifer Fenn Lefferts can be reached at email@example.com.