Urban streams are increasingly threatened by eutrophication driven by anthropogenic pressures, particularly nutrient inputs from diffuse and point pollution sources. This study assessed the effectiveness of macrophyte-based phytoremediation as a Nature-based Solution for improving water quality in urban aquatic systems. Three native species – Typha latifolia L., Juncus effusus L., and Iris pseudacorus L. – were evaluated under controlled laboratory conditions for their capacity to remove nitrate (NO₃⁻), ammonium (NH₄⁺), phosphorus (P) and and phosphates (PO₄³⁻), followed by in situ application in the Costa/Couros Stream (Guimarães, Portugal), an urban stream historically affected by industrial and urban discharges.

During 8-week laboratory assays, all species achieved complete nitrate removal (100%), whereas the control achieved only 33.4%. Phosphorus removal efficiencies reached 100% for J. effusus, 98.5% for I. pseudacorus, and 96.0% for T. latifolia, outperforming the control (71.1%). Similar trends were observed for phosphate removal – 100%, 98.5%, and 96.1%, respectively – significantly exceeding the 65.7% recorded in the control. Significant differences were confirmed for I. pseudacorus and J. effusus. Ammonium removal ranged 85–88%, with no significant statistical differences. Plants exhibited normal growth, particularly for T. latifolia and I. pseudacorus.

Field implementation demonstrated the feasibility of phytoremediation in an urban context, though invasive species and human disturbances locally constrained plant establishment. Monitoring general physico-chemical parameters indicated stable water quality, with no deterioration trends. Overall, the results indicate that macrophyte-based phytoremediation holds strong potential to mitigate eutrophication in urban streams, provided that proper management and long-term monitoring are ensured.