The Llangollen and Montgomery canals are the modern names of branches of the Shropshire Union (SU) system and lie partially in Wales.

The "SU main line" runs southeast from Ellesmere Port on the River Mersey to the Staffordshire and Worcestershire Canal at Autherley Junction in Wolverhampton.

With two connections to the Trent and Mersey (via the Middlewich Branch and the Staffordshire and Worcestershire Canal) the SU is part of an important circular and rural holiday route called the Four Counties Ring.

Instead the northern Wirral section was joined to the pre-existing Chester Canal; eventually becoming part of the network Shropshire Union.

The canal passes alongside the city walls of Chester in a deep, vertical red sandstone cutting.

After Nantwich basin, a long sweeping embankment incorporating an aqueduct carries the canal across the main A534 Nantwich-Chester road.

The lengthy embankment is equipped with flood gates at both ends to prevent loss of water should the canal be breached in this area.

At Wheaton Aston, the canal climbs its last lock to reach the summit level, fed by the Belvide Reservoir just north of Brewood.

The link with the Staffs and Worcester provides a choice of onward journeys: The Shropshire Union Railways and Canal Company was formed in 1846.

Then (in 1847), the latter was taken over by the London and North Western Railway Company, which allowed the Shrewsbury Canal and the branch from Norbury Junction to decline.

One boat close to the 12 metres (39 ft) deep hole had to be evacuated, and minor damage to one local's garden was recorded.