Why is river, lake water discolored after rain, and what impact does it have?

Why is river, lake water discolored after rain, and what impact does it have?

Recent and ongoing storms have drenched much of the Brazos River basin, resulting in heavy runoff of water from land into streams, rivers and reservoirs. This has resulted in an abundance of sediment flowing into the water.

The United States Geological Survey says that the material that causes water to be turbid consist of clay, silt, sand, algae, plankton, and other substances.

“During periods of low flow, many rivers are a clear green color, and turbidities are low,” according to the USGS. “During a rainstorm, particles from the surrounding land are washed into the river making the water a muddy brown color, indicating water that has higher turbidity values. In addition, during high flows, water velocities are faster and water volumes are higher, which can more easily stir up and suspend material from the streambed, causing higher turbidities.”

Sources of turbidity can include soil erosion, waste discharge, urban runoff, eroding stream banks, large numbers of bottom feeding fish, -- which can stir up sediment, excessive growth of algae, microorganisms and land development.

There are some consequences caused by extra sediments in the water, such as an increase in the cost of treating drinking water, and possible degradation of fish habitat.

What impact does turbidity have on water quality?

“Excessive turbidity, or cloudiness, in drinking water is aesthetically unappealing, and may also represent a health concern,” according to the USGS. “Turbidity can provide food and shelter for pathogens.” Fortunately, according to the U.S. Environmental Protection Agency, water treatment processes have demonstrated that they can effectively remove the pathogens caused by turbidity.

The Texas Commission on Environmental Quality requires drinking water providers to notify their customers when turbidity reaches a certain level, and may require them to issue boil water notices to customers in cases where equipment fails to properly purify the water. Fortunately, the TCEQ notes, turbidity does not necessarily pose an immediate threat to public health.

Although turbidity is naturally occurring, it definitely increases when storms roll through, stirring up sediment in the water. The good news is that once the storms begin to subside, the impact of turbidity will start to diminish as well.

So how long should you expect turbidity remain in the Brazos Basin? It depends on a number of factors, such as location and if additional rainfall results in runoff. A certain amount of turbidity is normal for all rivers, but some areas of the Brazos River basin are more turbid due to their overall geology.

While it may take several weeks or even months depending on the location, turbidity in water conditions will eventually subside. For more information on turbidity, click here.