This study tested water treatment wetlands in an urban park located in São Paulo, Brazil. Eichhornia crassipes (water hyacinth) was introduced into two creeks inside the park, to assess the efficacy of wetlands in treating flowing waters. The plant adaptation to local conditions was very good. Higher removals were obtained in Total Suspended Solids, Turbidity and Color (maximum removal > 70%); TKN, Total Phosphorus and Fecal Coliforms had satisfactory removals (maximum removal > 50%). BOD presented low removals and Dissolved Oxygen was consumed, indicating that aerobic processes occurred. Despite the experiment’s difficulties and results’ variance, the study shows that water hyacinth has potential to treat flowing water, especially when there’s an urgent need for meeting sanitary and aesthetical standards in urban parks.