Great Lakes are estimated at 900 trillion. The influx of parasitic lamprey populations after the development of the Erie Canal and the much later Welland Canal led to the two federal governments of the US and Canada working on joint proposals to control it. By the mid-1950s, the lake trout populations of Lakes Michigan and Huron were reduced, with the lamprey deemed largely to blame. This led to the launch of the bi-national Great Lakes Fishery Commission. "The Great Lakes: An Environmental Atlas and Resource Book" (1972) noted: "Only pockets remain of the once large commercial fishery." But, water quality improvements realized
Aire and Calder Navigation Narrow Canals, and the Rochdale Canal. The Selby Canal connects to the Ouse, from where boats can travel upstream to reach York, Boroughbridge and Ripon, or downstream to the River Derwent. Beyond Goole are the Humber and hence Hull, Immingham, and the North Sea. The Sheffield and South Yorkshire Navigation, which can be reached via the New Junction Canal, forms a link with Doncaster, Rotherham and Sheffield to the south west, and the tidal River Trent at Keadby to the east. In the early 1600s, the River Aire was navigable to Knottingley, and boats carrying up to 30 tons traded