The coca fields are planted along the contours of the land with little terracing and the fields are kept bare of plants except for the coca or poppy plants. These methods, in combination with the steep slopes, serve to strip away topsoil with every strong wind and heavy rain, very quickly making the fields infertile not only for further cultivation but for jungle plant life as well. Recent observers over-flying the jungle describe it as a patchwork quilt of green broken by patches of gray desolation. In addition to causing soil infertility, the topsoil runoff fills waterways and rivers with sediment changing their courses, causing flooding, and killing fish and aquatic plant life by lowering the oxygen content of the water and smothering the river bottoms. Locals who used to depend on the large fish in the rivers for food, no longer find any fish large enough to eat.
Pollution is also a factor in the environmental destructiveness of coca and poppy cultivation.
The pesticides used by the growers travel through the soil into the ground water and eventually into the rivers and streams. Pesticides are inherently toxic to the insects but they can also harm larger animals and people in greater concentrations. Fish and other aquatic life are particularly susceptible to this contamination. The fertilizer in the water encourages the algae to grow at increased rates while killing the organisms that feed on it. As a result, the algae overwhelms other aquatic plant life and restricts water flow.