Knockoneil River, Inveroe River, Agivey River, Aghadowey River, Macosquinn River, Ballymoney River and Articlave River. The water level on the Lower Bann is controlled by the Rivers Agency using gates situated at Portna (near Kilrea) and The Cutts at Coleraine. History Ptolemy's Geography (2nd century AD) described a river mouth called Αργιτα (Argita, "shining"), referring to the Bann. The Lower Bann provides the only outlet for Lough Neagh, the largest freshwater lake in the British Isles, which is fed by six major rivers, including the Upper Bann. The ability of the lake to absorb large quantities of flood water is limited, and consequently, the areas around the lake are prone to flooding. The Lower Bann encountered a large shoal of rock at Portna, which reduced the effectiveness of the outflow, and in 1738, Francis Hutchinson, the Bishop of Down and Connor petitioned the Irish Parliament to do something about the shoals, and hence the annual flooding that affected his people. Although Parliament responded encouragingly, no actual work was done, and the problem remained. In 1822, the Scottish engineer Alexander Nimmo proposed a radical solution. The Newry Canal provided a route southwards from Lough Neagh to Carlingford Lough, but it rose to a summit and then descended again. His proposal was to lower the summit level so that it was below the level of Lough Neagh, remove all the locks, and so provide a second outlet to the sea. Not only would it solve the problems of flooding, but would also solve the inadequate water supply for the canal, eliminate lock maintenance, and could generate around 2,200 kW as the water would still have to fall by . The plan was a little too ambitious, and failed to win support. In 1842, the Board of Works were authorised by an Act of Parliament to carry out works in the Lough Neagh basin, which would improve navigation, drainage and milling. A series of public meetings were held, and a survey was made of the Lower Bann. The Board of Works then instructed their own engineer to carry out a survey. John McMahon estimated that it would cost £183,775 to improve the Lower Bann from Lough Neagh to the sea, and that the navigation works accounted for less than half of this, with the drainage works making up the rest. Removal of the Portna shoal would reduce the level of the lake surface