The stream network is poorly developed and widely spaced, with major rivers carving valleys that are relatively deep and steep-sided. Almost all of the natural lakes of Iowa are found in the northern part of this region (the Iowa Great Lakes). Most of the region has been converted from wet prairie to agricultural use with substantial surface water drainage. Only a small fraction of the wetlands remain, and many natural lakes have been drained as a result of agricultural drainage projects via drainage tiles or ditches.