Employee & co-worker were organizing the laydown yard, including stacking 16"" culverts. EE was lifting from one end of the 20 ft culvert while the co-worker was lifting from the opposite end. While lifting, EE felt pain in his lower back. He reported the accident to his Supervisor the next day 6-13-07 but did not seek treatment until 6-22-07. Diagnosed with lumbar muscle strain.