Point source pollution originates from a single identifiable source, like a pipe or drain. Non-point source pollution has diffuse sources and is caused by rainfall or snowmelt picking up pollutants over an area and depositing them into waterways. Common point source examples include industrial wastewater discharges, while non-point sources include agricultural runoff and urban runoff from cities. Monitoring pollution involves detecting and measuring contaminants, and can use direct methods like sampling or indirect methods like a biotic index that examines the types of organisms present.