Torrential valleys in the area of Nature Park Učka create torrential streams which are formed under the influence of the amount of water in nature. Characteristics of torrential streams are usually determined by the amount of rainfall in a particular period of the year. Torrential brook Potok flows mountainside Učka and flows into the Adriatic Sea in the village Medveja. Macroinvertebrates are organisms sensitive to variations of aquatic habitats and with the usual chemical / microbiological analysis, used to evaluate the quality of water within the biological monitoring of freshwaters. The aim of this study was to compare the quality of water of brook “Potok” in the area of Lovranska Draga determining the Biotic Index (BBI) and the measurement of basic chemical and physical parameters through the two-year period (years 2013. and 2014.). Indicator species of macroinvertebrates were collected by “kick-sampling” method and returned after observing and determining. Air and water temperatures were measured using a mercury thermometer. Chemical analysis of the water was performed by using semi-quantitative commercial test "model Educa". Biotic Index for water of Potok based on the collected indicator species of macroinvertebrates was 9,7 in year 2013., and for year 2014. it was 8,75. Water temperature in year 2014. was 9,8˚ C, while in year 2013. was higher by four degrees, and also the air temperature in year 2013. was higher by 6 degrees and it was 22˚ C. values for the chemical parameters are equal, except the concentration of NO₂⁻ ions which was less than 0.02 ppm in year 2014., and in year 2013. was zero. According to the calculation of Biotic Index and semi-qualitative chemical analysis water of torrential brook “Potok” it is in the group of naturally pure water.