Question: The 39 mi long river which flows through the Irwell Valley in North West England and forms the boundary between Manchester and Salford meats what other river at Waterfoot, Lancashire?

Context articles: Salford, Greater Manchester
River Irwell
River Ceiriog
Pendleton Fault
Mersey and Irwell Navigation
Manchester Exchange railway station
Waterfoot, Lancashire
Irwell Valley
Clifton Country Park
List of tributaries of the Lackawanna River

Salford ( ) is a city lying at the heart of the City of Salford, a city and metropolitan borough of Greater Manchester, in North West England.
 Salford is sited in a meander of the River Irwell, which forms in part its boundary with the city of Manchester to the east.
 The Salford wards of Broughton and Kersal are on the other side of the river.
 Together with its neighbouring towns to the west, Salford forms the local government district of the City of Salford, which is administered from Swinton.
 The former County Borough of Salford, which included Broughton, Pendleton and Kersal, was granted honorific city status in 1926; it has a resident population of 103,886 and occupies an area of 8.1 sqmi .
 The wider City of Salford district has a population of 219,200.
The River Irwell ( ) is a 39 mi long river which flows through the Irwell Valley in North West England.
 Its source is at Irwell Springs on Deerplay Moor, approximately 1.5 mi north of Bacup.
 It forms the boundary between Manchester and Salford and empties into the River Mersey near Irlam.
The River Ceiriog (Welsh: "Afon Ceiriog" ) is an 18 mi long river in north east Wales.
 It is a tributary of the River Dee.
 It rises at an altitude of around 1800 ft on the south east slopes of Moel Fferna in the Berwyn Mountains, and flows through the Ceiriog Valley in Wrexham County Borough.
 It flows below Chirk Castle and the town of Chirk, where the Chirk Aqueduct carries the Llangollen Canal over the river.
 The Ceiriog joins the Dee east of the town.
 In its lower reaches the river forms the border between Wales and Shropshire in England.
 Home to a Trout fishing club, the river and its valley were described by British Prime Minister David Lloyd George as "a little bit of heaven on earth".
 As well as being a home to trout the first grayling to be artificially reared in Wales were released into the river in 2009.
The Pendleton Fault, sometimes called the Irwell Valley Fault, stretches for about 20 mi from Bolton in Greater Manchester along the Irwell Valley through Pendleton to Poynton in Cheshire, running northwest–southeast.
 The fault throws the beds of the Middle Coal Measures of the Manchester Coalfield by 1000 ft on its western side.
 The fault is active, and movement has caused earthquakes.
 An earthquake of intensity 6 on the Richter scale that occurred on 10 February 1889 was felt over an area of 2500 sqmi .
 Lesser shocks were recorded in the early 20th century, in 1931 and 1944.
 Coal mining in the Irwell Valley between Bolton and Pendleton may account for small movements, although all mines in the area closed in 1929 and no coal has been mined since.
The Mersey and Irwell Navigation was a river navigation in North West England, which provided a navigable route from the Mersey estuary to Salford and Manchester, by improving the course of the River Irwell and the River Mersey.
 Eight locks were constructed between 1724 and 1734, and the rivers were improved by the construction of new cuts several times subsequently.
 Use of the navigation declined from the 1870s, and it was ultimately superseded by the Manchester Ship Canal, the construction of which destroyed most of the Irwell section of the navigation and the long cut between Latchford and Runcorn.
Manchester Exchange railway station was a railway station located in Salford, immediately to the north of Manchester city centre.
 It served the city between 1884 and 1969.
 The main approach road ran from the end of Deansgate near Manchester Cathedral, passing over the River Irwell and Chapel Street; a second approach road led up from Blackfriars Road.
 Despite its name, the station was located just over the Manchester/Salford boundary (River Irwell) in Salford, and only the 1929 extension to Platform 3 was east of the Irwell in Manchester.
Waterfoot is a small Rossendale mill-town between Rawtenstall and Bacup in Lancashire, England, where the B6238 road from Burnley meets the A681 road.
 It is where the River Whitewell meets the River Irwell.
The Irwell Valley in North West England extends from the Forest of Rossendale through the cities of Salford and Manchester.
 The River Irwell runs through the valley, along with the River Croal.
Clifton Country Park is a local nature reserve in the Irwell Valley at Clifton, Greater Manchester, North West England.
 Situated next to a double bend in the River Irwell, it is north east of the Manchester to Preston railway line and the A666, Manchester Road, Clifton where it is accessible via Clifton House Road opposite Clifton Cricket Club.
 Junction 16 of the M60 motorway is only about ¼ mile away to the south east.
The Lackawanna River is a 40 mi long river flowing into the Susquehanna River with 65 named tributaries, of which 33 are direct tributaries.
 The river flows through Susquehanna, Lackawanna, and Luzerne Counties in Pennsylvania.
 The shortest tributary is 0.4 mi long, while the longest is 21 mi long.
 The tributaries include 40 creeks, 14 brooks, 9 runs, and 2 rivers. By length, the five largest tributaries are Roaring Brook, Spring Brook, the East Branch Lackawanna River, Stafford Meadow Brook, and the West Branch Lackawanna River.
 By watershed area, the five largest tributaries are Spring Brook, Roaring Brook, the East Branch Lackawanna River, Leggetts Creek, and the West Branch Lackawanna River.