Members of OARS — the Organization for the Assabet, Sudbury, and Concord Rivers — are seeking volunteers to join the group’s annual river cleanup on Saturday. The nonprofit organization has been working with Northborough residents for 26 years to help clean the Assabet River, which runs through town, and can always use more help. Volunteers will meet at the Ellsworth McAfee Park on Route 135 at 9 a.m. to begin the cleanup. Volunteers should wear long pants, and shoes that can get wet and dirty. OARS is also seeking residents who can bring a canoe to help with the cleanup. To sign up, call OARS at 978-369-3956. The cleanup will finish around noon and be followed by a pizza party. The event will take place rain or shine.