This paper presents information on the hydraulic efficiency of wetlands and ponds, and examines the differences and similarities between degrees of mixing, short-circuiting and dead zones. It reports the pollutant removal performance of over 50 wetlands and ponds over the range of macrophyte cover from 100% (densely vegetated wetlands) to 0% (ponds). Not surprisingly, there exist performance continua, characterized by a smooth transition from fully vegetated to unvegetated systems. Factors influencing the choice of ponds, wetlands or combinations are examined. Wetlands are more efficient, and can produce lower TSS. Both wetlands and ponds can provide BOD, FC and ammonia removal, with ponds being better choices at high loading rates.