The refuge covers a 140 km long section of the river, from Łomża to Pułtusk in the geographical region of the Lower Narew Valley. From the east, it borders the Przełomowa Dolina Narwi refuge. The Lower Narew Valley refuge consists of several wide arcs. From Łomża, the river turns north-west gradually south-west and flows in a widening valley. The banks of the valley become asymmetrical. The left is the steep edge of the Międzyrzecze Łomżyńskie plateau, on the right the slope gently turns into long sandur slopes. In the vicinity of Różan the landscape changes. The right bank becomes higher. The valley cuts into the gentle elevation of the Ciechanowska Plateau, becomes 3 km wide, and the river heads clearly west. Then, making a sharp arc, it turns south again. The bottom of the Narew valley is occupied by communities of aquatic plants associated with oxbow lakes, reed beds, peat bogs and meadows. The steep, sunny slopes of the valley are occupied by thermophilic grasslands, and the more fertile sites by oak-hornbeam forests with a dominance of pine and a share of oak, hornbeam and lime. At least 35 species of birds have been recorded in the Lower Narew Valley refuge.