National Geographic Society (Washington, D.C.), WQED (Television station : Pittsburg, Pa.), & Seamans, J. (1991). Great lakes, fragile seas [videorecording]. The Society.
Cita Chicago (17th ed.)National Geographic Society (Washington, D.C.), Pa.) WQED (Television station : Pittsburg, i Joe Seamans. Great Lakes, Fragile Seas [videorecording]. Washington, D.C: The Society, 1991.
Cita MLA (9th ed.)National Geographic Society (Washington, D.C.), et al. Great Lakes, Fragile Seas [videorecording]. The Society, 1991.
Atenció: Aquestes cites poden no estar 100% correctes.