A study of the Allain's Creek Ducks Unlimited impoundment, a coastal salt marsh impoundment located near the town of Annapolis Royal, Nova Scotia, was carried out during 1993. The primary objective of the study was to determine the basis for the high waterfowl productivity of the impoundment through a comprehensive analysis of the physical, chemical and biological nature of the system over the course of one growing season. Phytoplankton primary production within the impoundment is very high and indicative of a hypereutrophic system. Levels of both phosphorous and nitrogen were very high and seldom appeared to be limiting. There was little evidence that these nutrients originate from outside of the impoundment and it is suggested that the productivity of the system is driven mainly by high phosphorous concentrations stored within sediment that accumulated prior to impoundment of the salt marsh. Nitrogen inputs appear to be largely allochotonous originating from nitrogen fixing cyanobacteria which were observed to produce extensive phytoplankton blooms. Periphyton growth rates and submersed macrophyte biomass are also high and probably play an important role in supporting secondary producers. Secondary producers were found to be present in high numbers, were characterized by low species diversity as a result of the brackish nature of the impoundment, and were composed mainly of organisms considered to be important food sources of waterfowl brood.