Jatibarang Reservoir is one of the new reservoirs in Semarang. To prevent the degradation of reservoirs water quality in the future, it is important to measure the dam water fertilization periodically. Like one of the ways to determine the level of fertility of the dam water is by measuring the primary productivity of the water and chlorophyll-a and physic-chemical parameters of the waters. This study was conducted from February to March 2016 in Semarang Jatibarang Reservoir. The aim of this study is to determine the primary productivity of waters based on depth difference and the depth effects on primary productivity of the waters of the Jatibarang reservoir, Semarang. The method used in this study is descriptive method. Sampling locations are station I; Inlet, Station II: middle of reservoir and stations III: Outlet with three repetitions for the period of one week. The results of primary productivity measurements at each stations per depth is; at the depth of 0 m the results ranges from 54.750 to 90.000 mgC/m3/day, at the depth of 5 m from 91.500 to 102.750 mgC/m3/day, at the depth of 10 m from 39.750 to 64.500 mgC/m3/day and at the depth of 15 m from 20.250 to 45.5000 mgC/m3/day. Based on these results, it is concluded that the water of Jatibarang Reservoir is classified as Mesotrofik-eutrophic waters. The average value of chlorophyll-a in the first week is 0.6913 mg/m3, in the 2nd week is 0.6665 mg/m3, and the 3rd week is 0.4409 mg/m3. The results of simple regression test reveals that there is a significant effect of water depth and chlorophyll-a on primary productivity is 51.3%.