The coral reef was discovered by joint Iraqi–German expeditions of scientific scuba divers carried out in September 2012 and in May 2013. Prior to its discovery, it was believed that Iraq lacks coral reefs as the local turbid waters prevented the detection of the potential presence of local coral reefs. Iraqi corals were found to be adapted to one of the most extreme coral-bearing environments in the world, as the seawater temperature in this area ranges between 14 and 34 °C. The reef harbors several living stone corals, octocorals, ophiuroids and bivalves. There are also silica-containing demo-sponges. In the rural areas of the alluvial plain and in the lower Diyala region, settlement almost invariably clusters near the rivers, streams, and irrigation canals. The bases of the relationship between watercourse and settlement have been summarized by Robert McCormick Adams, director of the Oriental Institute of the University of Chicago. He notes that the levees laid down by streams and canals provide advantages for both settlement and agriculture. Surface water drains more easily on the levees' back-slope, and the coarse soils of the levees are easier to cultivate and permit better subsurface drainage. The height of the levees gives some protection against floods and the frost that often affect low-lying areas and may kill and/or damage winter crops. Above all, those living or cultivating on the crest of a levee have easy access to water for irrigation and household use in a dry, hot country. Although there are some isolated homesteads, most rural communities are nucleated settlements rather than dispersed farmsteads; that is, the farmer leaves his village to cultivate the fields outside it. The pattern holds for farming communities in the Kurdish highlands of the northeast as well as for those in the alluvial plain. The size of the settlement varies, generally with the volume of water available for household use and with the amount of land accessible to village dwellers. Sometimes, particularly in the lower Tigris and Euphrates valleys, soil salinity restricts the area of arable land and limits the size of the community dependent on it, and it also usually results in large unsettled and uncultivated stretches between the villages. Fragmentary information suggests that most farmers in the alluvial plain tend to live in villages of over 100 persons. For example, in the mid-1970s a substantial number of the residents of Baqubah, the administrative center and major city of Diyala Governorate, were employed in agriculture.