Loss of streamside shade and reduced summer flows further contribute to stream warming. Herbicides and pesticides likewise are important pollutants in both rural and urban areas. Metals, hydrocarbons, and other toxic chemicals are more specific to urban runoff. Indus-trial discharges have been strictly regulated over the last 20 years, and most of the worst problems have been cleaned up. Now the everyday actions of individuals contribute a greater share of urban runoff pollution.
Vehicles are probably the single worst offenders.
Because brake pads and tires wear directly onto roads, the metals and other contaminants that they deposit are transported very efficiently to the stormwater system. Vehicles are also the leading source of hydrocarbons in urban runoff. Oil and other automotive fluids are constantly leaking onto roads and parking lots. In fact, urban gardeners use up to 10 times more toxic chemicals per acre than farmers. Harm to aquatic life Not surprisingly, the cumulative effects of urbanization are devastating to aquatic life.