A controlled feeding study and field collections of duck feces were used to examine the potential of ducks for dispersing wetland plant species in the prairie pothole region of North America. To determine how long seeds of wetland species remain in their digestive system, captive mallards were fed known quantities of seed of either Atriplex patula, Chenopodium album, Chenopodium rubrum, Echinochloa crusgalli, Polygonum spp., Scirpus acutus, Scirpus validus, or Sparganium eurycarpum. Fecal samples were collected hourly from ducks for 24 to 30 hours after seeds were ingested. On average, 23% of the seeds ingested were recovered intact, and 36% of these were still viable. In other words, only 7% of the seeds ingested were still viable when they were evacuated, with a range from 1% for Echinochloa crusgalli to 16% for Scirpus validus. The mean passage time of seeds was 7.6 h, with a range of 5.1 h for Echinochloa crusgalli to 11.1 h for Chenopodium rubrum. Nearly all seeds were evacuated after 24 to 30 h. Seed size and seed coat strength (lignin content) were negatively correlated with the probability of a viable passage but not correlated with passage rates. After ingestion, mallards are estimated to be able to transport internally viable seeds up to 1,400 km but more typically 20 to 30 km. Field collections of duck feces at five locations in the prairie pothole region confirmed that ducks are dispersing intact seeds of common wetland species (Carex sp., Echinochloa sp., Panicum sp., Polygonum spp., Potamogeton spp., Salix sp., and Scirpus spp.). There were between 0.3 to 5.2 intact seeds per duck. Only 1.6% of this intact seed of four taxa (Carex sp., Potamogeton spp., Salix sp., and Scirpus spp.) germinated under greenhouse conditions. Although any given duck is carrying only a few viable seeds, the millions of ducks moving among wetlands, especially during spring and fall migrations, collectively are effective dispersal agents for many wetland plant species.