Evaporation is one of the most important climatic phenomena in arid and semi-arid areas which causes water loss from the surface of water reservoirs. About 4.8 billion cubic meters of evaporation from reservoirs of dams occurs in Iran. Therefore, optimal use of available water resources is necessary due to the high cost of water supply, population growth and global warming. It is also important to measure the amount of evaporation from the surface of open reservers in water resources management. Floating covers are one of the methods to reduce evaporation from surface water reservoirs. These coatings help to reduce evaporation by protecting against the entry of solar radiation and a physical barrier to the removal of water. In the first part of this research, in order to estimate the evaporation rate of the Zayandehrood Dam on a daily and monthly basis, the empirical methods of Meyer, Henfer, Shahtin, Marciano, Penman, Stephens-Stewart, Ivanov, USBR, DeBruin, Priestley-Taylor and Linacer were used. Also the results of each method were compared with the measured evaporation from the pan. Based on comparisons of RMSE, MBE, NRMSE, R 2 and d between methods and evaporation pan, it was found that for daily evaporation, the Linacre method and for monthly, the Ivanov and DeBruin methods were more accurate. After the Linacre method, the methods of Meyer and Penman were ranked second and third, respectively, for estimating daily evaporation. Also after the Ivanov and DeBruin methods, the USBR method is also accurate for estimating the monthly evaporation from free water surface. The superiority of the Linacer method shows the effect of temperature on evaporation from the free surface of water. The purpose of the second part of this research is to determine the effect of concrete floating covers (Perlite, Leca 2-4 and Leca 4-10) on surface water. In this section, to investigate the performance of Perlite, Leca 2-4 and Leca 4-10 floating covers in reducing evaporation from free surface water, the water level is measured from September to November. The results of measured evaporation in form of a randomized complete block design with three replications (three types of coverage and an uncovered) were analyzed in SAS software. The analysis of data show that there was significant effect on reducing evaporation from the covered reservoir. The maximum rate of evaporation from uncovered reservoir is 16.5 mm/day and in tanks covered with Perlite and Leca2-4 and Leca4-10 were 11.2, 9.52 and 10.41 in September, respectively. Results show that the Perlite and Leca2-4 and Leca4-10, can reduce amount of evaporation by 33.86%, 42.70% and 38.49%, respectively. The results showed that perlitic floating covers have better performance in reducing evaporation from free water surface. Key words : Reduce Evaporation, Zayandeh Rood River, Concrete Balls, Leca, Experimental Method