Stormwater ponds and wetlands are used to clean up dirty water in cities. A review of 58 studies found that not all ponds and wetlands work the same. Some are better at removing pollutants than others. To clean water well, ponds and wetlands need to be designed with certain features like pretreatment, long flow paths, and the right shape. The type of pollutant also affects how well they work. Sediment is easiest to remove, followed by trace metals, phosphorus, and nitrogen. Future research should focus on improving these systems.