Columbia Island is in part natural, and in part man-made. Columbia Island did not exist in 1818 and at that time, Analostan Island (now known as Theodore Roosevelt Island) was largely rock and quite close to the D.C. shoreline. Due to deforestation and increased agricultural use upstream, the river eroded much of the northern bank and widened the gap between Analostan Island and the shore and simultaneously large deposits of silt built up around Analostan Island. By 1838, Analostan had almost doubled in length toward the south and by 1884, the new southern part of Analostan Island was defined and built up, and supported a well-established wetland. However, the river gradually eroded the center of Analostan Island, severing Columbia Island from its parent body.