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EPA: Nutrient Runoff Is Widespread Waterway Stressor

Source: EPA

The NRSA found that the percentage of river and stream miles in poor biological condition could be reduced by 20% if excess nutrient levels could be reduced from poor to good or fair,” said the report.

Four of every 10 miles of U.S. rivers and streams are in poor condition because of nitrogen and phosphorus runoff, said the EPA in its latest National Rivers and Streams Assessment. “The NRSA found that the percentage of river and stream miles in poor biological condition could be reduced by 20% if excess nutrient levels could be reduced from poor to good or fair,” said the report.

“Nationally, 28% of river and stream miles were in good biological condition while almost half were in poor condition,” said the EPA. Excess nitrogen levels was found in 44%, excess phosphorus in 42%, and excess riparian vegetation cover in 27% of river and stream miles. The report, based on a 2019-20 survey of stream conditions, was released in late December to little notice. Only 35% of stream miles had healthy fish communities.

Nutrient runoff is “a difficult problem that is concentrated in agricultural regions that drain into the Mississippi River,” said The Associated Press. The Midwest director of the Environmental Working Group told the AP that new water quality regulations were needed, rather than voluntary efforts.

Less than one-third of our river and stream miles (28%) had healthy biological communities, based on an analysis of benthic macroinvertebrate communities.

  • Biological condition was based on the abundance and diversity of benthic macroinvertebrates (bottom-dwelling invertebrates such as dragonfly and stonefly larvae, snails, worms, and beetles).
  • Close to half of river and stream miles (47%) were in poor condition.

Just over one-third (35%) of river and stream miles had healthy fish communities.

  • Fish community health was based on fish abundance and diversity.
  • Sixteen percent of river and stream miles were not assessed for fish. The remainder (49%) were in fair and poor condition.

Nutrients (phosphorus and nitrogen) were the most widespread stressors.

  • Forty-two percent of the nation’s river and stream miles were in poor condition, with elevated levels of phosphorus, and 44% were in poor condition for nitrogen.
  • Poor biological condition was more likely when rivers and streams were in poor condition for nutrients.

Reducing nutrient pollution could improve biological condition.

  • NRSA analyses indicated that approximately 20% of the river and stream miles in poor biological condition could be improved if nutrient condition changed from poor to fair or good. The level of improvement was estimated to be similar regardless of nutrient and biological indicator analyzed.

Healthy habitat occurred in over half of our river and stream miles.

  • Physical habitat indicator scores revealed that 68% of river and stream miles were rated good for in-stream fish habitat, 57% scored good for streambed sediment levels, and 56% of river and stream miles had good ratings for riparian vegetation (vegetation on or adjacent to the river or stream banks).
  • However, 64% of river and stream miles had moderate or high levels of riparian disturbance.

Bacteria exceeded EPA’s recreational benchmark in 20% of river and stream miles.

  • Enterococci, bacteria that indicate fecal contamination, were above EPA’s benchmark in 20% of river and stream miles.
  • Swimming and recreating in water contaminated with pathogens could make people ill.

Algal toxins were present, but at very low levels, with minimal recreational human health concerns.

  • Microcystins and cylindrospermopsin were detected in 9% and 10% of river and stream miles, respectively, but did not exceed EPA recommended criteria in any samples.

Contaminants were present in all fish tissue, but risk varied by contaminant and fish consumption levels.

  • In samples composed of fillet tissue from multiple fish, concentrations exceeded screening levels as follows (as a percentage of the 41,099 river miles comprising the sampled population):
    • Mercury: 26%
    • Total PCBs: 45% for general fish consumers, 74% for high-frequency fish consumers.
    • Additionally, PFOS was detected in 91% of the 290 fish composite samples analyzed for NRSA 2018-19. EPA is not currently comparing PFOS concentrations in fish to screening levels because the toxicity assessment used to calculate screening levels is draft. When the assessment is final, EPA intends to update the PFOS information provided in this report to include screening level exceedances.


The National River and Streams Assessment 2018-19 is available by clicking HERE.

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