There are two tunnels at Harecastle.
The first was dug under the direction of James Brindley during the construction of the Trent & Mersey canal between 1766 and 1777. Brindley died in 1772 so never saw it finished, the remainder of the work being overseen by George Henshall. It was 2880 yards (2663m) long and had no towpath, boatmen having to "leg" their boats through. The entrance to the Brindley tunnel can be seen at the left of the first photo, the current entrance is to the right.
Due to the high volume of traffic in the early 1800's, it was decided to commission a second tunnel. This was undertaken by Thomas Telford and was completed in 1827. It was 2926 yards (2528m) long and was provided with a towpath for horses to tow the boats through. Initially, this new tunnel was used in conjunction with the old tunnel, each being used for a different direction. During the early 20th century, it suffered from subsidence and was closed in 1914 to traffic after a roof collapse.
An electric tug was introduced around the time of the collapse of the Brindley tunnel and continued until 1954 when a large fan was introduced at the southern end to permit the passage of diesel boats without asphyxiating the steerers. This tunnel also suffered from subsidence as was closed between 1973 and 1977. The derelict towpath was removed some time after 1979 to allow boats extra headroom in the centre of the tunnel.
The second photo shows the northern portal of the Telford tunnel. The orange colour of the water is due to iron oxide seeping from the Brindley tunnel (this is similar to Worsley where the iron oxide from the Duke of Bridgwater's mines seeps into the canal.