The natural drainage channel for carrying off the overflow of the Nile, now the Bahr Yûsuf, being situate in the lowest lying lands, would of necessity be kept clear by the annual discharge of the waters from the inundated lands. On reaching the south end of the isolated piece of desert in front of Lahûn, part of its discharge would go east of this island, part to the west. The western discharge would, at Lahûn, either enter the Fayûm, or part would do so and part continue northwards. At the north end of the isolated piece of desert, the discharge, going northwards, would again divide up, some of it continuing to flow in the channel under the Libyan Desert, some finding its way back to the Nile near Wâstah. Under these circumstances the channel north of Lahûn would not be so likely to keep itself clear as the channel to the south of Lahûn. Thus the channel conducting the water to the Fayûm would remain clear, while that carrying the outflow would be less likely to do so. The outflow would also be more within soil (i.e. below the land surface) than the inflow and therefore under worse conditions for keeping its channel open. The outflow channel might therefore deteriorate, and, as there would be water flowing in it during the hot season at a low velocity, reeds might grow and obstruct the water-way. The draining of the Fayûm Lake would therefore be unsatisfactorily done, and the water would stand in it at a comparatively high level till the end of the summer. This would encourage the growth of rushes also in the Lahûn-Hawârah passage, which would check the inflow, and, while preventing the rise of the lake, would favour silt deposit. “This then,” in Mr. Petrie’s words, “was the state in which the great engineering monarchs found the province:—a basin full of overflow Nile water, replenished at each inundation through a marshy shallow inlet and with much of its bottom so raised by deposits as to have become almost marsh ground, like the present lakes about the coast.” A channel to drain off the water at low Nile and reclaim the marshes would have been the first work to suggest itself, and the necessity for regulators, to prevent any excess of water from entering by the cleared channel, would then have been felt. The flow of water in the drain leading back to the Nile may have suggested the grand idea of utilising the lake as a regulator for the excesses and shortcomings of the Nile.