PRN 46668 Alvingham lock was built in 1767 by John Grundy. It is constructed of red brick with limestone ashlar dressings, wood and cast iron. The river Lud, running north to south, is culverted and passes under the lock by means of an inverted syphon. For the full description and the legal address of this listed building please refer to the appropriate List of Buildings of Special Architectural or Historic Interest. {1} This lock is one of six upper locks on the Louth Navigational Canal. Their design is almost unique, with only one other lock of this type in the country. {2}