Underwater noise pollution due to marine traffic can have adverse effects on marine animals. This is the first study of modeling underwater noise levels from shipping in the Slovenian Sea. The aim of the study was to select and develop an appropriate methodology for modeling underwater noise levels. The logarithmic model was used to describe the range-dependent attenuation of low-frequency sound. The parameters of the model were determined from the transmission loss function calculated along ten selected cross sections across the North Adriatic using the parabolic equation. The difference between the measured and modeled levels was within ±5 dB. However, the model was able to identify trends in underwater noise levels that could not be identified by the measurements, suggesting that noise maps could provide a basis for management purposes. In building the model, we found that the modeled values are mainly affected by the speed of the ships. Therefore, adjusting the speed of ships could be an effective measure to be taken into account for controlling underwater noise from shipping in the world’s seas and oceans.