the island and the eastern shore of the loch. The river then flows through Blantyre and Bothwell, where the ruined Bothwell Castle stands on a defensible promontory. As it flows past Uddingston and into the southeastern part of Glasgow, the river begins to widen, meandering through Cambuslang, Rutherglen, and Dalmarnock, and past Glasgow Green. From the Tidal Weir westwards, the river is tidal: a mix of fresh and salt water. The river has been artificially straightened and widened where it passes through the city centre. Although the new Clyde Arc now hinders access to the historic Broomielaw dockland area, seagoing ships can still come upriver by following the dredged channel as far as Finnieston, where the PS Waverley docks. From there, the river flows past the shipbuilding heartlands, through Govan, Partick, Whiteinch, Scotstoun, and Clydebank, all of which historically housed several major shipyards, of which only two remain today. The river then flows west, out of Glasgow, past Renfrew, under the Erskine Bridge, and past Dumbarton on the northern shore and the sandbank at Ardmore Point between Cardross and Helensburgh. Opposite, on the southern shore, is the last remaining Lower Clyde shipyard, at Port Glasgow. The river continues on to Greenock, where it reaches the Tail of the Bank as the river merges into the Firth of Clyde. Here at the mouth of the Clyde, there is currently a significant ecological problem of oxygen depletion in the water column. The strath of the Clyde was the focus for the G-BASE project executed by the British Geological Survey in the summer of 2010. Industrial growth The economic prosperity that the Clyde made possible at the beginning of the Industrial Revolution was due to the location of Glasgow, as a port facing the Americas. Tobacco and cotton trade began to drive this economic engine in the early 18th century. However, an obstacle to further economic growth soon became evident: the Clyde was too shallow for the largest ocean-going ships to navigate into it, so cargo had to be transferred, at Greenock or Port Glasgow, to smaller ships that could sail upstream into Glasgow itself. Deepening the Upper Clyde In 1768, John Golborne advised that the river should be made narrower and the scour increased by constructing rubble jetties and dredging sandbanks and shoals. Another obstacle to navigation that had to be solved was that the river divided into two shallow channels by