Lock 31 on Pennsylvania's Delaware and Hudson Canal was one of a series of locks that raised and lowered canal boats as the waterway climbed and descended between Honesdale, Pennsylvania, and Kingston, New York, a total elevation difference of 972 feet managed through 108 locks whose lifts were generally eight to twelve feet. The locks were numbered westward from Kingston to Lackawaxen and then from Lackawaxen to Honesdale, though boatmen often used names, and this lock was also known at different times as Newcastle, New Castle, Weir's, and O'Han's. Locks also served as dams that maintained water levels above and below each chamber, and at this site the lock tender was responsible for keeping a six-foot level below the lock, aided by a sluiceway that diverted water around the closed gates when the lock was idle. The lock's thick stone walls were lined with wooden planks fastened to vertical beams and iron ties anchored in the masonry, and some of those beams and bolts still remain visible. During the canal's seventy years of operation, the total number of locks changed because John Roebling's aqueducts at Lackawaxen, Cuddebackville, and High Falls altered the route in 1848, and because the double lock at Honesdale could be counted as one or two. Locks were also dangerous places, with moving machinery and rushing water causing serious injuries and delays, including a drop-gate failure reported in 1877 and crushing injuries to boatmen reported in 1858. Originally, both ends of the locks used balance-beam gates that required two men to operate independently, but after 1850 the upper gates were replaced with a drop gate and hand-operated machinery that allowed one person to work both upper and lower gates from a shanty on the lower gate bridge near the lock tender's house. During the canal's enlargement between 1841 and 1851, boats were made larger to carry more coal, and locks were lengthened from seventy-six feet to ninety feet by moving the lower gates, leaving two sets of gate recesses in the wall. Water entered and left the lock through paddles or wickets in the gates, and the practiced process of locking through usually took twelve to fifteen minutes, contributing about twenty-nine hours of locking time to a round trip, with the cycle repeated day after day except on Sundays.