McMahon, a scheme was developed to make the Lower Bann navigable from Lough Neagh to the sea. This involved removing a great shoal of rock at Portna which had the effect of lowering the level of Lough Neagh by around . This had a significant effect on the Blackwater, and major work was required on the river to keep it navigable. The Maghery Cut, which gave access to Lough Neagh to the south of Derrywarragh Island, had to be made deeper and wider, and the channel of the river was dredged, to maintain a navigable depth. The final lock on the Coalisland Canal and the Ulster Canal had to be reconstructed with a lower sill and deeper gates, to accommodate the lower level of the river, as did the final lock on the Newry Canal where it joined the Upper Bann. The total cost of the project, split between navigation and drainage work, was estimated at £183,775. The cost of work on the Blackwater exceeded that on any of the other inflows to Lough Neagh. While the first of the river above the lough was large and wide, considerable work was needed between there and Blackwatertown to eradicate sharp bends and shoals. New sections of river channel were cut, and were made between wide, with their depth sufficient to provide of water when Lough Neagh was at it lowest designed level during the summer months. Excavated material was used to backfill the old river channels, so that loss of land was reduced. To protect the surrounding low-lying land from flooding by the river, the channel was embanked. The embankments were designed with self-acting sluices, to allow watercourses to pass through them when water levels were suitable. After some of the embankments had been finished, local landowners petitioned against their completion, as they felt that the lower level of Lough Neagh and the works already carried out gave them sufficient protection, and it was inadvisable to completely protect the land. The work on defences was thus deferred. The original plans were to embank the Tall River and the Callan River, which joined to the south of Clonmain and flowed into the Blackwater below Charlemont bridge. This aspect of the project was reworked, and a new straight cut was made from a point on the Tall River to the north of Clonmain, crossing Sir William Verner's bog, and rejoining the Blackwater just