Stara Nida represents one of the three hydrological channels traversing the Nadnidziański Landscape Park, a locale characterized by ecological diversity within the Nida valley, Poland. Historically rendered inactive due to flow regulation, this specific river branch underwent restoration in February 2023 as a pivotal component of the "Restoration of the Inland Delta of the Nida River" project. The revitalization of Stara Nida has precipitated beneficial ecological metamorphoses within the landscape. To evaluate the impact of the restoration of the Stara Nida branch on the physicochemical characteristics of water in the landscape, systematic sampling of regional SW and GW was conducted. The sampling duration covered a 12-month period, segmented into two phases: the first six months leading up to the restoration (from February 2022 to July 2022) and the subsequent six months following the restoration of the Stara Nida branch (from February 2023 to July 2023). A total of 114 water samples were collected from 10 distinct sampling locations. In-situ measurements of key indicators, including temperature (T), electrical conductivity (EC), dissolved oxygen (DO), pH, and total dissolved solids (TDS), were performed using handheld devices. Concurrently, laboratory analyses were carried out for total nitrogen (TN), total phosphorus (TP), chloride (Cl–), sulfate (SO42–), manganese (Mn2+), iron (Fe2+,3+), zinc (Zn2+), cadmium (Cd2+), lead (Pb2+), copper (Cu2+), and chemical oxygen demand (COD). Statistical analyses encompassed the Shapiro–Wilk test (α = 0.05) and the Wilcoxon (Mann–Whitney) rank sum test (α = 0.05) to discern significant disparities in physicochemical indicators at sampling points pre- and post-restoration of the Stara Nida branch. Additionally, Pearson correlation analysis (α = 0.001) was employed to evaluate overarching changes at the sampling points attributable to the impact of the Stara Nida branch restoration.