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2023 Results – Pyrethroid TMDL Update 

2023 Results – Pyrethroid TMDL Update 

Pyrethroid and Water/Sediment Toxicity Results to Date 

The California Rice Commission collects data on pyrethroids and toxicity in water and sediments at our four main agricultural drain sites in accordance with the Basin Plan Amendment Total Maximum Daily Loads (TMDL) requirements under the Clean Water Act. Pyrethroids (i.e., Warrior, Lambda-cy, Silencer) are used in rice production to manage insects.

On May 30, 2023, water monitoring data results indicated detection of pyrethroid and a statistically significant mortality (toxicity) at the Colusa Basin Drain near Colusa. This same location had similar results in 2021. According to the TMDL, we anticipate that these two results at the same location within a 3-year window will require the implementation of a management plan. In addition, a statistically significant mortality (toxicity) occurred in June 2023 in sediment analysis at Sacramento Slough near Karnak. The corresponding water toxicity test indicated no statistically significant mortality (toxicity). Further testing is being conducted.

For more information, contact the CRC’s Industry Affairs Manager Craig Riddle at criddle@calrice.org or (916) 812-3468.

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Rice Water Quality Programs Monitoring Update
Water Quality •

Rice Water Quality Programs Monitoring Update

Monitoring for 2025 is halfway complete.

The 2025 surface water monitoring under the RPP and WDR programs is ongoing.

For the Rice Pesticide Program (RPP), there have been a handful of detections in late May, none of which were above the agricultural drain performance goal.  The latest results from early June were non-detectable.  

The Rice Waste Discharge Requirements (WDR) surface water program is in an assessment year, which means additional sampling for pesticides and toxicity.

Pyrethroids used in rice have been reported in association with water toxicity at the upper Colusa Basin Drain this year for multiple events.  The California Rice Commission (CRC) sent out letters earlier this year requesting the use reporting information (to be submitted in the fall) for pyrethroid users in the area.  Algal water toxicity was reported in the Sacramento Slough near Karnak as well.  

The CRC continues to work on behalf of the industry to conduct required monitoring and interface in reporting with the Water Board.  Additional efforts are underway to assess and analyze water quality trends across the valley and gather information from industry on uses and operational patterns.

We appreciate the industry’s support of the regulatory programs and their good stewardship of the commercial products used and protection of the environment.

For more information, contact the CRC’s Industry Affairs Manager Craig Riddle at criddle@calrice.org.