When the Salford Docks were redeveloped significant changes were made to the configuration of the waterways. Dock Number 9 was blocked off from the canal by a causeway. The former railway bridge was relocated to the middle of the new basin created. It was situated in the middle creating the Huron and Erie Basins.
Dock Number 8 was also blocked off from the canal but this time it was equipped with a lock to allow boats to access the Ontario Basin. Dock Number 7 was split into three basins called the St. Francis, St. Louis and St. Peter Basins. A new canal was created to allow water access between each of the basins. It is indicated by the arrow on the map below.
The canal passes through residential developments and is well served by footpaths and footbridges.
I gather that the name of the canal isn't, as you might expect, connected to the past function of the port. It was named in honour of Rifleman William Mariner of the King's Royal Rifles. He was awarded the Victoria Cross for bravery in France in 1915. Mariner's Canal was opened officially by The Duke of York in 1989.