The Słupia River in the urbanized section within the limits of Słupsk was investigated in terms of lamprey fish presence. Among 25 studied sampling sites only 5 were inhabited by the discussed species in autumn and 4 in summer, all in the very center of the city. The investigated lamprey fish representatives preferred slightly transformed sites with considerable water oxygenation and fast water flow. No L. planeri representatives were noticed up the Szczecin-Gdańsk bridge, therefore its frequency reached 16% in summer and 20% in autumn. During the summer study 5 representa-tives of the brook lamprey were noticed, while in autumn 10, with no distinct sexual features but with developed suckers and fins, which indicated the metamorphosis starting in summer and last-ing until the next year spring spawning. The caught brook lampreys were between 130 and 176 mm long and weighed from 0.9 to 14.7 g. Average length and biomass were higher in autumn and reached consequently 156 mm and 6.3 g comparing to 142 mm and 1.2 g in spring.