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
Thames and Severn Canal and remains the fourth longest. There were always problems with water supply, as no reservoirs were built, while the summit section near the tunnel ran through porous limestone, and there were constant difficulties with leakage. Competition from the railways took much of the canal's traffic by the end of the 19th century, and most of the canal was abandoned in 1927, the remainder in 1941. Since 1972, the Cotswold Canals Trust has been working to restore both the canal and the Stroudwater Navigation, so that it can again provide a navigable link between the Thames and the Severn. A number