Stormwater from rain events is itself very clean. However, once it hits the ground, it begins to collect the contaminants and pollutants it encounters on its journey to the bay or ocean. Coronado has a very robust program to capture these pollutants before they reach the receiving waters. The City uses "best management practices," guidelines created to reduce pollutants from reaching receiving waters, including frequent street sweeping, diverting dry-weather flows to the sewer system, use of perimeter runoff controls at construction sites, and other approved techniques.