The arrival of railways in the area did not immediately affect its traffic, but the failure of the iron industry in 1875 and increasing subsidence due to coal mining led to it becoming uneconomic.

Most of the route was buried by the construction of the A4059 road in 1923, although a short section at the head of the canal remains in water and is now a nature reserve.

The act also empowered the company to build tramroads to any mines, quarries or works within 8 miles (13 km) of the route of the canal and railway.

[7] The company leased some limestone quarries at Penderyn, and conveyed the stone along the tramway to the Hirwaun Ironworks and to their own lime kilns.

Having reconstructed and expanded it, he gradually bought out the Aberdare Canal Company, to ensure the route for his goods, and owned 96% of the shares by 1826.

This was financed by selling eleven shares, with additional costs being met from revenue, with the result that no dividend was paid in 1826.

An entrepreneur called Thomas Powell started another pit at Tyr Founder in 1840, and hit the Four Foot seam two years later.

Fifteen more pits were sunk in the Cynon Valley between 1840 and 1853, and a number of basins and tramways were constructed to facilitate export of the coal.

In 1845, the company decided to build a pumping engine at Tyr Founder, to supply water from the Afon Cynon to the canal just above Cwmbach lock.

[16] In 1864, the Great Western Railway built a line to Middle Duffryn (later renamed Mountain Ash), and further depleted the trade in coal on the canal.

In 1888, 102,805 tons of goods were carried, but the rates were low in order to encourage use of the canal, and the income did not cover the running expenses.

[17] By 1897, the volume of traffic had dropped to 7,855 tons, and passage along the canal was extremely difficult, as a result of bridges and towpaths sinking.

Water was supplied to the top pound by the feeder from the Afon Cynon, and later by the pumping engine at Tyr Founder.

There were a total of seven overflow weirs, to allow surplus water to return to the river, and a stop lock before the junction with the Glamorganshire Canal.