On-site observations of hydrological and meteorological parameters of regions with harsh climatic conditions after the creation of hydro developments [i, 2] showed that in the winter extended stretches of rivers with an open water surface form downstream of hydrostations, which are the cause of occurrence of heavy advection-radiation fog (steam fogs).In the presence of air temperatures below -12 to -15~ moderate winds (up to 12 m/sec), and sufficiently high humidity, a cold air mass flows onto the warm water surface having a temperature above 0~which promotes the formation of steam fog, which changes the conditions of heat exchange of the water with air, affects both the length of the polynya and climate of the region, possibility of occurrence of smog, icing of cables, and creates difficulties in the operation of air and water transport.A reduction of steam fog over the open water surface in the winter would solve to a considerable extent the problem of the negative effect of a hydrostation on the environment.When working on this problem it is necessary:i. To calculate the size and configuration of the zone of steam fog over the polynya in relation to the water temperature and meteorological factors and to evaluate the effect of the steaming process on the intensity of heat exchange of water with air.2. To determine how steaming affects the ice and thermal conditions of the lower pool and in what stretches the precipitation of steam fog is most effective.3. To recommend ecologically clean methods which can be used for this purpose.To solve the stated problems by mathematical modeling methods, it is necessary to examine a system taking into account the interaction of the thermal regime of the river and atmospheric boundary layer. However, since the thermal regime of a river is considerably more inertial than the atmosphere, as a first approximation the given problem can be solved separately and the mutual effect of the water and air can be taken into account by means of an iterative procedure.Heretofore the ice and thermal regime in the lower pool of hydro developments was calculated for constant meteorological characteristics, which were taken on the basis of a statistical analysis of long-term series of observations at weather stations.In this case, transformation of the air flow over the open water surface and the effect of steam fog on the intensity of heat exchange of the water with air were not taken into account.Steam fog forming in the winter over a nonfreezing polynya is supercooled (to between -15 and -20~ is liquid, is in a metastable state, and can crystallize under an artificial action.The effect of artificial crystallization of fog on the ice conditions of the flow in the lower pool is examined in this work.Two mathematical models were used for this purpose.The first model for calculating disturbances of the microclimate as a result of natural evolution and artifical crystallization of low clouds and fogs was developed at the Central Aerological Observatory (TsAO) [3][4][5]. The second model of the...