In literature on wetland design it is often recommended to use design elements to improve the hydraulic performance, which is linked to the pollutant removal efficiency. To investigate the effect these elements have on the hydraulic performance, a case study was carried out on two wetlands located in southern Sweden. The two main questions of the study were how the performance differs between the two wetlands and how it is affected by the use of deep zones and islands. Field measurements and computer simulations were carried out to obtain residence time distributions (RTD) and flow patterns. As analytical parameters, normalized peak time and effective volume ratio were used to interpret the results. The conclusion is that islands and deep zones as design elements can improve the hydraulic performance, but also that it is important to use them wisely. In one of the wetlands, the bad location of several islands led to severe short-circuiting and large areas of dead zones.