Sediment is mineral or organic solid matter that is washed or blown from land into lakes, rivers, or streams. It can clog systems, fill in lakes and wetlands, and smother aquatic life such as fish eggs and insects and damaging fish gills. This can disrupt the entire food chain, and cause great damage to an ecosystem. Sediment can also carry toxic chemicals

Nutrients are essential for plant and animal growth and nourishment, but the overabundance of certain nutrients in water can cause a number of adverse health and ecological effects. Nutrients can be bad for a lake if excessive enrichment causes an algal bloom. This abundance of algae eventually produces a large amount of decomposing organic matter, which depletes oxygen from the water, which can kill fish.

Public health concerns include safe water that does not contain harmful pathogenic (disease-causing) microorganisms in concentrations that could cause illness.

E. coli is normally found in human and animal intestines, and is the most reliable indicator of fecal contamination in water. Its presence in drinking water represents a health concern because they are usually associated with sewage or animal wastes. (need better discussion)

Natural stream purification processes require adequate oxygen levels in order to provide for aerobic life forms. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis.

High water temperatures stress aquatic ecosystems by reducing the ability of water to hold essential dissolved gasses like oxygen