The channel of the River Clyde between Glasgow and the natural deepwater of the open sea in its natural state was shallow and filled with shoals and sandbanks. As the town's trade expanded the wish to use the river for trade increased. In 1556 the first recorded attempt was made to deepen the channel, but met with little success. A century later Cromwell's commissioner Thomas Tucker observed that "Glasgow was checked and kept under by the shallowness of her river, every day more and more filling up".
Frustrated by the shallows Glasgow constructed a new harbour downstream at Port Glasgow and by the end of the 17th century this was the main trading port for the town. The rapid development of Glasgow's trade in tobacco which followed the 1707 Treaty of Union provided renewed impetus for an efficient transport link between the town and the sea. In 1736 the town council agreed to fund "an experiment" to remove the sandbanks, but it was not until 1752 that a mathematician called John Stirling suggested that the depth of water be increased not by lowering the river bed but by raising the water level by the construction of a series of dams or weirs.
This idea was progressed by John Smeaton, the first true civil engineer, who proposed a dam at the Marlin Ford near Renfrew. To allow vessels to pass through the dam Smeaton proposed a lock with a length of twenty-one metres. The scheme was agreed and in 1759 Parliament gave approval to what was to become the first of many acts allowing the deepening of the Clyde.
A start was made on the construction of the dam and lock but winter floods and the difficulties of construction caused work to be abandoned within a few years. A new approach was needed and this was forthcoming with the arrival in Glasgow in 1768 of the Cheshire canal engineer John Golborne.