The complex structure of karst areas has beneficial effects on forming extended hydrogeological networks with highly developed underground flows. The paper addresses the body of the Rijeka-Bakar underground waters extending from highlands region of Gorski Kotar to the littoral. Climate, geological and hydrogeological characteristics of the area are set forth as well as springs confluences of the town of Rijeka and Bakar Bay. Grobničko polje is particularly addressed as multiannual data were available because of monitoring conducted for the purposes of flood defense and water protection. Kikovica and Ponikve are the selected locations since there are data available from monitoring levels of underground and surface waters for the period from 2017 to 2023. Software packages Excel and R were used for comparison of underground and surface water levels at each location as well as to compare underground waters levels. Apart from multiannual periods, one-month dry periods and high water periods are set forth. Data analysis corroborated the results from the previous researches: filling of underground aquifers results in outpouring of water to the surface and formation of periodic floodplains at both locations. Regression analysis confirmed exceptional correlation between the levels of underground and surface water levels in conditions of complete saturation of underground, R=0,94 (p<0,001) at location Kikovica and R=0,97 (p<0,001) at location Ponikve. Water discharge from Kikovica area (approx. 300 m above sea level) towards Ponikve (approx. 100 m above sea level) where the water is retained longer and extension of drainage zone from Grobničko polje to Bakar Bay were both confirmed.