The effect of passage of Najas marina L. seeds through the digestive system of the common mallard duck (Anas platyrhynchos) on their germinability was investigated. Most of the seeds (∼70%), which were consumed by the birds were digested. However, germination of the remaining seeds was remarkably improved. Germination of seeds whose seed coats were mechanically cracked was also higher than that of the controls and equalled the germination percentage of the mallard-treated seeds. Seeds of Najas are retained in the diegestive tracts of mallards for over 10 hours. Thus, as mallards are strong flyers, the seeds of Najas may be distributed over long distances.