The relative resource value and use of the Estuary and Firth of Clyde have varied through time. Until the eighteenth century the estuary was difficult to navigate. The firth, with its rich fishing grounds and sheltered harbours, was the focus of early settlement. However, increasing trade with the Americas, larger ships and growing competition between Glasgow and the more accessible ports of Greenock and Dumbarton stimulated plans to improve the navigability of the estuary. This was achieved by deepening and widening the main channel, a process which continued as the size of ships increased and more sophisticated techniques of river improvement developed. Within a century and a half the bed of the estuary was transformed from an obstacle to navigation into a major water-route, from which the largest passenger liners in the world were launched.
Since the Second World War the relative resource values of the estuary and the firth have changed with the increase in air travel, the decline of ship building and heavy industry on the Clyde, and the increase in the size of cargo vessels. The economic focus shifted from the estuary to the natural, deepwater harbours of the firth.
At present redevelopment of derelict docklands and industrial sites along the estuary is taking place, while the firth is suffering from the effects of economic recession. Planning is now being increasingly directed toward the development of the amenity, recreational and tourist potential of both the estuary and the firth.