This runoff often contains harmful substances such as toxics, excess nutrients and sediments. This characteristic makes it all the more difficult to control. Sediments are soil particles carried by rainwater into streams, lakes, rivers and bays. By volume, sediment is the greatest pollutant of all. Its caused mainly by erosion resulting from bare land, poor farming practices, and construction and development.
Nutrients are substances which help plants and animals live and grow.
Fertilizer and animal waste are the main sources of these substances. Toxic substances are chemicals which cause human and wildlife health problems. They include organic and inorganic chemicals and metals, pesticides, formaldehyde, household chemicals, gasoline, motor oil, battery acid, roadway salt and so on. Pathogens are disease-causing microorganisms present in human and animal waste. Most pathogens are bacteria.