We conducted a mark-recapture study of Siren intermedia in a wetland in southeastern Missouri that is intensively managed for waterfowl. Over a 9-month period, we examined population characteristics, growth rates, and spatial activity. Density and standing crop biomass estimates were 1.35 to 2.17 sirens/m² and 44.9 to 72.2 g/m². Juveniles comprised 39% of the population. Adult males were significantly larger in both total length and mass than adult females. Sirens from our population had relatively low growth rates compared to some populations in other areas. Smaller individuals tended to grow faster than larger individuals. Maximum distance between captures did not differ significantly among juveniles and adult males and females. Home ranges of adults overlapped considerably and were highly variable in size, ranging from 1 to 232 m². Sirens can be the dominant vertebrate in many wetland communities, and their natural history and spatial ecology should be considered in management decisions.