"In the Indus period the Saraswati river system may have been even more productive than that of the Indus, judging by the density of settlement along its course. In the Bahawalpur region, in the western portion of the river, settlement density far exceeded that elsewhere in the Indus civilization . . . While there are some fifty sites known along the Indus, the Saraswati has almost a thousand . . . [The Yamuna] shifted its course eastward early in the second millennium, eventually reaching its current bed by the first millennium, while the Drishadvati bed retained only a small seasonal flow; this seriously decreased the volume of water carried by the Saraswati. The Sutlej gradually shifted its channel northward, eventually being captured by the Indus drainage . . . The loss of the Sutlej waters caused the Saraswati to be reduced to the series of small seasonal rivers familiar today. Surveys show a major reduction in the number and size of settlements in the Saraswati region during the second millennium."