Water pollution is the contamination of water bodies (such as lakes, rivers, oceans, and groundwater) by various substances, which can have harmful effects on human health and the environment. There are many different types of pollutants that can cause water pollution, including:

1. Chemical pollutants: These can include toxic substances such as pesticides, industrial chemicals, and heavy metals. They can come from a variety of sources, including factories, agricultural runoff, and sewage treatment plants.

2. Biological pollutants: These are microorganisms such as bacteria, viruses, and parasites that can cause waterborne diseases. They can be found in untreated sewage, animal waste, and runoff from farms.

3. Nutrient pollutants: Excessive amounts of nutrients such as nitrogen and phosphorus can cause algal blooms and deplete oxygen levels in the water, leading to fish kills and other negative effects on aquatic ecosystems. These nutrients can come from agricultural runoff, fertilizers, and sewage.

4. Physical pollutants: These are materials such as sediment, silt, and debris that can clog waterways, disrupt aquatic habitats, and cause flooding. They can come from construction sites, erosion, and landfills.

The causes of water pollution are numerous and can vary depending on the location and type of water body. Some of the most common causes of water pollution include:

1. Industrial activities: Many industries produce large quantities of wastewater that can contain harmful chemicals and pollutants. If not properly treated, this wastewater can be discharged into nearby water bodies, causing pollution.

2. Agriculture: Agricultural activities such as fertilizer and pesticide use can contribute to nutrient and chemical pollution in waterways. Animal waste from livestock operations can also be a major source of water pollution.

3. Sewage and wastewater treatment: Untreated sewage and wastewater can contain harmful microorganisms, chemicals, and nutrients that can cause water pollution. Even treated wastewater can still contain trace amounts of pollutants that can be harmful.

4. Stormwater runoff: During heavy rainfall, stormwater can pick up pollutants from roads, parking lots, and other surfaces and carry them into nearby water bodies.

5. Household waste: Improper disposal of household waste such as cleaning products, pharmaceuticals, and personal care products can contribute to water pollution.

Overall, water pollution is a complex and multifaceted issue that requires comprehensive solutions at the local, regional, and global levels. Addressing the causes of water pollution and reducing the amount of pollutants entering our waterways is essential for protecting human health and the environment.