###### Abstract  
The construction of new, artificially snowed, ski slopes and the accompanying infrastructure changes the natural environment and exerts pressure on the ecosystems. This study examined the impact of the construction and operation of a new ski slope, with its infrastructure and artificial snow production, on the quality of nearby stream waters. The research period covered the time before, during and after the slope construction. Electrolytic conductivity (EC) and pH were measured on-site, chemical analyses included the determination of Ca\({}^{2+}\), Mg\({}^{2+}\), Na\({}^{+}\), K\({}^{+}\), HCO\({}_{3}\)-, SO\({}_{4}\)\({}^{2-}\), Cl\({}^{-}\), NO\({}_{3}\)\({}^{-}\), and microbiological analysis comprised mesophilic and psychrophilic bacteria, total and fecal coliforms, and _E. coli_. As a result of intensive environmental transformations, the examined parameters varied significantly over the study period, as shown by the coefficient of variation. Due to land cover changes, concentrations of all the examined parameters increased during the ski slope construction due to ions and bacteria leaching from the soil. However, when construction works were finished, all bacterial and some chemical indicators returned to the state observed before the construction, most probably due to the recovery of vegetation and self-purification of water. Supply of melt water from artificial snow, produced from water containing higher concentrations of ions, increased pH, EC, Ca\({}^{2+}\), Mg\({}^{2+}\) and HCO\({}_{3}\)\({}^{-}\) in the stream. Providing that the development of ski stations is unavoidable in the considered region, conducting studies assessing the impact of new ski slope construction is an important step that should be conducted prior to undertaking such investments. ski resort; ski slope; snowmaking; stream water; water quality Article  
Impact of Construction and Functioning of a Newly Built Ski Slope on the Quality of Nearby Stream Water  
1  
[PERSON], [PERSON], [PERSON]. The reduced quality of water within ski resorts results from contamination of rivers and streams by nutrients and microorganisms from treated human waste but also from runoff from ski slopes, roads, car parks, etc. [2]. Undoubtedly, the functioning of ski areas affects the natural environment in a wide range of aspects. Construction of ski-related facilities requires the removal of native vegetation and top soil, therefore increasing erosion, surface runoff and nutrient leaching [1]. [PERSON] et al. [3], in a case study in Vermont, attributed increased runoff in the area to forest harvesting, increased soil compaction and snow redistribution. The same authors reported elevated concentrations of sodium and chloride in nearby stream waters as the result of using de-icing road salt on the access road to the ski resort. Additionally, [PERSON] and [PERSON] [4] in their study on the effect of the Santa Fe ski area on the water quality, found that the concentrations of every major nutrient except SO\({}_{4}\) were increased below the ski area as a result of using road salt. They also reported increased erosion and sediment transport. Another negative aspect of the functioning of ski resorts is that they mostly become four-season facilities, therefore water demand is also elevated during the entire year [3]. However, water consumption by residential and resort facilities may be small compared to the demand for snowmaking in winter, which is particularly dangerous as, in winter, water resources are generally lower, therefore baseflow becomes more severe. The production of artificial snow may also have a number of other effects on the water ecosystems resulting in, e.g., different properties of artificial snow compared to the natural snow [5]. Artificial snowmaking increases the amount of water in the watershed, increasing the peak flow and suspended sediment yield [6].