Irrigated Agriculture Practices Protective of Aquatic Life in the Sacramento Valley

Thursday, Jun 15th, 2023

By Mike Trouchon and Stephen Clark

The latest water quality monitoring results from the Sacramento Valley Water Quality Coalition (Coalition) demonstrate once again that management practices used by the 8,600 farmers of irrigated agriculture continue to protect the aquatic ecosystem and the fish and wildlife in the region.  These practices ensure water quality is favorable for fish and wildlife in the region, which includes bugs and other food sources as part of the ecosystem.

Toxicity testing for sensitive algae, invertebrates, and fish is commonly used as a tool to assess the biological condition of waterbodies.  Toxicity tests by certified laboratories are used in the Central Valley Regional Water Quality Control Board’s regulatory programs as a tool to evaluate potential effects on aquatic life beneficial uses under the Porter-Cologne Water Quality Control Act.

As the chart above indicates, there have been 1,465 water column and sediment samples collected and analyzed from 22 waterbodies (see map for monitoring locations) throughout the Sacramento Valley over the period 2012-2023. In summary, the figure shows:

  • No toxicity to Pimephales (fathead minnow);
  • Extremely rare toxicity to Ceriodaphnia (water flea) and Selenastrum (algae); and
  • Infrequent toxicity to Hyalella, a shrimp-like invertebrate that feeds on algae and diatoms and is a major food source for waterfowl along the Pacific Flyway.

Starting in 2012, the Coalition began regularly testing sediments collected in the Sacramento Valley for toxicity to Hyalella, as pyrethroid pesticides in sediments have the potential to cause toxicity to Hyalella.  Toxicity to the invertebrate in sediments is observed when tests show statistically significant toxicity and an effect greater than (>) 80% of the laboratory control sample. The Hyalella sediment test is the only one among the five tests shown in the above figure where only the statistically significant results less than (<) 80% of the control (red layer of stacked bars) are considered an exceedance of the Basin Plan’s narrative toxicity objective.  Since 2012, 191 sediment samples have been tested with Hyalella and 18 have triggered the analysis of pyrethroids in the sediment.  Of those 18 samples analyzed, eight (8) contained pyrethroid pesticides at concentrations sufficient to cause or contribute to the observed toxicity to Hyalella.

Beginning in 2020, the Coalition was required to begin testing water column samples to determine their toxicity to Hyalella as required by the Central Valley Water Board’s Central Valley Pyrethroids TMDL and Basin Plan Amendment.  Out of a total of 73 water column samples tested to date for toxicity to Hyalella, 13 showed some reduction in the survival of the organism as compared to the control sample, and six (6) of those samples contained pyrethroid pesticides at concentrations sufficient to cause or contribute to the observed toxicity to Hyalella.

Water leaders in the Sacramento Valley closely evaluate the results from this testing as part of their sustainability objective to manage water and land uses for multiple beneficial uses (e.g., farms, fish, birds, cities and rural communities and recreation). In this case, the focus is on assuring that agronomic practices are protective of aquatic life beneficial uses of water that support fish, birds, and wildlife. Here, the results suggest that the management practices used by the 8,600 owners and operators of irrigated agriculture are largely working and continue to protect aquatic ecosystems that are important to fish, birds, and other wildlife. The results also indicate a healthy biological condition for these waterbodies, which generally support a wide variety and high number of macroinvertebrate taxa, including many that are critical for supporting fish and wildlife. In areas where there are noticeable detections, the local leaders analyze the results with the Coalition’s scientists, seek to identify the source of toxicity, and then determine what actions upstream can rectify any problems.

For more information on this data and the program for improving water quality in the Sacramento Valley, please visit the Coalition’s website at

Mike Trouchon is an Associate Scientist with 30 years of experience in the water quality field, with recent assignments focused on management and coordination of a regional agricultural water quality monitoring program in the Sacramento Valley and characterization of salinity conditions in the Central Valley.
Stephen Clark has conducted extensive research 34 years in aquatic ecotoxicology with an emphasis on the effects of contaminants on aquatic organisms at the whole organism/cellular/biochemical level (e.g., “biomarkers”).

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