Flooding events — the American Bottom is a floodplain, and extreme flood events would have been catastrophic for the dense settlements occupying it — have also been proposed as a contributing factor, with some geological evidence supporting the occurrence of major floods during the period of Cahokia’s decline.

The agricultural demands of supporting a large urban population may have contributed to environmental degradation that reduced the land’s long-term productivity.

Archaeological evidence for significant deforestation around Cahokia has been proposed, based on the quantities of wood required for construction and fuel, and deforestation would have had multiple negative effects: increased erosion, reduced wildlife habitat, changes in the local hydrology.

The borrow pits that pockmarked the landscape around the mounds altered drainage patterns.