Differences in the Turbidity Between Wastewater & Stream Water

Wastewater is released back into the environment in a limited number of ways. It is either treated or not treated and then released into streams, lakes, oceans or applied to land. The turbidity of wastewater---its muddiness, opaqueness or levels of sediment and pollution---can be either higher or lower than the turbidity of the receiving water body depending on a variety of factors.

Turbidity of Wastewater

• The turbidity of wastewater depends on whether it has been treated and to what level it has been treated. Untreated sewage has a high turbidity, while treated wastewater effluent from a modern treatment plant will typically have very little turbidity.

Turbidity of Streams

• The turbidity of streams varies greatly depending on geographical, seasonal and human-impact variables. Mountain streams are very clear most of the year, but during high flow in the spring, can be very turbid. Slow-flowing swamps are naturally very turbid. Nearby human activities such as farming, construction and mining can increase the turbidity of streams.

Significance

• The turbidity of streams has major impacts for wildlife living in those streams. Very turbid wastewater being released into a clear stream can choke out and kill fish and the macroinvertebrates that form the base of the stream's food chain.

Misconceptions

• One common misconception is that incoming wastewater is always more turbid than the receiving stream. Treated wastewater flowing from a modern wastewater treatment plant can have much lower turbidity than the stream it flows into.

Other Considerations

• Turbidity is not the only concern with wastewater entering streams. Wastewater, even after treatment, can contain harmful levels of nutrients and other chemicals that can have negative impacts on the environment.