When a lake is brown, it usually indicates that eutrophication is occurring. This process refers to premature aging of a lake when a “megadose” of nutrients are added to the water, usually due to run-off that is either contaminated by agriculture or industry. Due to this rich supply of nutrients, blue-green algae begin to take over the green algae in the lake, disturbing the food webs and leading to an eventual loss of fish. When a lake is blue, this usually means that the lake has been damaged by acid precipitation. The gradual drop in pH is most often caused by exposure to acid rain, causing the disruption of the food webs and eventually killing most organisms. The end result is clear water, which is an indication of the lake’s low productivity.