Point source pollution is from a defined source like a factory pipe or discharge from a waste water treatment plant. Nonpoint source pollution is also called runoff. Runoff pollution cannot be easily traced to a single source or point of origin. This runoff occurs when rainwater or snowmelt contacts soil, organic wastes, fertilizers, and other pollutants carrying them to surface and groundwater. Soluble nutrients and those attached to soil particles come from parking lots, roads, livestock lots, and crop fields. These nutrients and sediments are deposited in streams, marshes, and lakes causing reduced water-holding capacity, increased oxygen use, and accelerated plant growth. As plants die and decompose oxygen is consumed. If too little oxygen is left in the water resource fish kills may occur.