Serum and fecal samples from 12 species of aquatic birds were studied for evidence of exposure to a hemagglutinating duck adenovirus (DAV). DAV is serologically indistinguishable from egg-drop syndrome-76 virus. A total of 285 serum samples were tested by the hemagglutination-inhibition (HI) test. Forty-two percent of the birds had HI antibodies, with titers ranging from 8 to 256. Wild ducks showed the highest frequency of antibodies (56%) while in coots and grebes, antibody was less frequent, 33% and 26%, respectively. Attempted virus isolations from 79 fecal samples were unsuccessful. The data support the hypothesis that DAV is indigenous in wild duck populations and suggest that infection and viremia are limited in time and occur at a very early age.