Construction of dams and reservoirs, diverting of large volume of river water for irrigation, industrial and municipal water supply drastically change hydrological and hydrochemical regimes of the rivers. In river valleys the soil and vegetation deprived of the regular floods become subjected to degradations. However, the most dramatic changes in the natural environment occur in the deltas of river with regulated flow in arid and semi-arid regions. Here, because of reduction of water inflow into delta and alleviation of flooding, the landscapes suffer a severe drying and desertification. Delta lakes dry-up, ground water table becomes lower, soil and ground water salinity increases. Toxic salts accumulated on the surface of desertifying soils are carried off by the wind to the neighboring areas. All these processes we investigated in the Ily River delta in South-Eastern Kazakhstan. The construction of Kapchagay reservoir (28.1 km3) in 1970 appeared an epoch-making event in the management of land and water resources of the Ily's basin. By the 1980, the irrigation lands here reached 300 thousand hectares. With the filling up of the Kapchagay reservoir and irrigation development the annual water runoff into the river delta was reduced by 3 km3, suspended solids runoff was reduced by15 million tons, water mineralization was increased by 20-30%. These changes worsened the delta's water feeding on the area about 8000 km2 and caused serious environmental degradations. Hydromorphic soil evolution caused by delta plain aridization begins from the evolution of soil regimes, especially water and salinity-related ones. Pedogenic processes forming soil properties are more conservative and change slowly, which is the reason why the rapid processes of delta aridization are inexorably encountered with a certain lack of agreement between soil properties and their morphological features. Our research showed that rapid diminishing of the delta's water feeding favors mainly the development of water regime specific to drying-up soils. The length of time during which such regime exist is, as an average, within 5-7 years. The further exhaustion of the delta's water feeding leads to the desertification of hydromorphic soils. These soils were formed from dried-up ones in the course of 5-6 years. Such a spell of time was approximately the same for the entire series of dried-up hydromorphic soils – from the alluvial-meadow to the swampy ones. The desertified soils are subjected to further evolution into zonal desert soils. Mainly takyr-like soils, solonchaks, and desert sands are formed on the bed-framing ridges. On the slopes of the lowland areas between the river beds, the forming soils are mainly takyr-like and solonchaks. The shortest period of zonal desert soils formation registered within 10-12 years, which is a significant regional feature connected with the light texture of local soils. The changes in agrochemical and physico-chemical properties caused by drying and desertification come about more slowly. Soil organic matter content with drying-up of meadow-series soils decreases, as an average, by 0.5%. In drying soils of the swampy series OM content at first increase by 0.5-1.5%. Further desertification of all hydromorphic soils leads to the reduction in humus content by 1-3%. The drying and desertificating of hydromorphic soils is accompanied by significant reduction of the C:N ratio in SOM (as an average from 15 to 8-10). Total nitrogen stocks in the soil do not diminish with drying and desertificating as quickly as SOM content. The essential patterns of changes detected by us in the soil-reclamation conditions of the Ily's delta as well as direction and intensity of changes in the water-salinity regime and properties of soils and ecologo-genetic evolution series of hydromorphic soils may serve as a scientific basis for ecological and soil reclamation related prognostification.