The tide in the estuary is very irregular. The south-east winds increase the flow and retard the ebb. When they are blowing, it often happens that the level of the water in the upper estuary keeps up from one tide to the next, sometimes for several days. The tide, which is slight at Montevideo, is greater at the bottom of the harbour on the Barra del Indio, sometimes rising nearly forty inches there. From there it advances with difficulty northward, over the Ortiz Bank, along the Uruguayan shore, whereas it passes freely into the deeper zone on the Argentine side.[134] At Buenos Aires it still has a depth of thirty inches. From there it advances northward by the Martin Garcia channels beyond the Playa Honda. The channel of the Pozos del Barca Grande, which crosses the Playa Honda bank from north to south, parallel to the edge of the delta, is oriented in conformity with the tidal currents and maintained by them. It is not attached to the river, and it is separated from the mouths of the Parana de las Palmas or the Parana Mini by shallows which are navigable only to small boats. The _Rias_ of the Uruguay, where the tide raises the water twelve inches, forms a sort of reservoir which, at the ebb, feeds a strong current round Martin Garcia and sweeps the channels there. [134] The current at high tide is stronger than at low tide, and it has shifted to the north-east the streams which find an outlet on this side. The work done for the improvement of the estuary includes the deepening to thirty feet of the Barra del Indio and the dredging of a straight channel from that point to Buenos Aires. Steamers of large tonnage going up the Parana leave this channel twenty-six miles east of Buenos Aires, and turn north in order to pass east of Martin Garcia, and enter the river by the Parana Guazu or the Parana Bravo. Since 1901 the Argentine Government has considered a plan of opening a direct route from Buenos Aires to the Parana de las Palmas, either by cutting an artificial canal at the foot of the cliffs, across the Tigre archipelago, or by using the channel of the Pozos del Barca Grande and cutting the narrow bar which closes the Parana de las Palmas below. If this were done, the ports of the Parana de las Palmas would have direct access to the sea. Moreover, the new route from the Parana to the Atlantic would be entirely within Argentine territory, out of range of the Uruguayan shore, and Buenos Aires would become a necessary port of call both on departure and return.