Cheonsuman Bay emerged as a habitat for migratory birds as a result of a reclamation project that was undertaken in 1984. A breakwater was built around this area, which created Ganwolho Lake and Bunamho Lake. Moreover, a vast agricultural land spanning 6,400 hectares was formed on what used to be a mud flat. The monthly average temperature of Cheonsuman Bay area between October and March is about 1.2 degree Celsius higher than inland areas at the same latitude because of its oceanic climate. Such geographical conditions have made Cheonsuman Bay an ideal wintering site for migratory birds.

Cheonsuman Bay is located midway along the migration route of birds migrating from northern Siberia or Manchuria to Southeast Asia. As a result, Cheonsuman Bay has become home to nearly 200 different species of migratory birds that can be watched all year round. In winter, the area becomes a wintering site for over 300 thousand ducks and wild geese, as well as a wide variety of endangered species like storks, spoonbills, mute swans, and white-naped cranes. Lucky birdwatchers might be able to witness the great spectacle created by tens of thousands of migratory birds flying in a flock over the Cheonsuman Bay area.