 The reduction of marshland again allowed for even more areas of cultivation to feed the increasing population.During the 19th century, technical progress (for example, the replacement of windmills by steam engines) led to further improvements in drainage, contributing to the drying-up of the valley downstream as far as Hesdin).In the last quarter of the 20th century the authorities became aware of the importance of the marshes and started trying to preserve them, having earlier contributed to their disappearance.