Susan River - Toxicity
H.U. 637.20

The Susan River originates from Silver and Caribou Lakes in southern Lassen County and flows easterly through McCoy and Hog Flat Reservoirs and the City of Susanville, ultimately discharging into Honey Lake. During 1990, US EPA testing on the Susan River identified toxicity to larval fish and the aquatic plant, duckweed. Toxicity was exhibited in several samples, and in 1996 the Susan River was placed on the Federal Clean Water Act Section 303(d) list of impaired waters for toxicity of unknown cause.

Further results indicate that the Susan River exhibits low to moderate levels of toxicity in some locations. Therefore, the Susan River will continue to be 303(d)-listed for "unknown toxicity", but a TMDL is not currently recommended as the appropriate regulatory response since the pollutant(s) causing toxicity has not been decisively identified. A collaborative process between the DPR and the Water Board to identify and address the pesticide use practice(s) responsible for the water quality violations will be implemented in accordance with the Management Agency Agreement between the State Board and DPR. Follow-up monitoring, including additional toxicity testing, will be needed to determine the effectiveness of control measures and need for additional regulatory action.

Numeric water quality objectives for the Susan River and its major tributaries are defined in the Basin Plan for total dissolved solids, chloride, sulfate, boron, nitrogen and phosphorus. Beneficial uses of the Susan River include:

  • Municipal and Domestic Supply (MUN)
  •  Agricultural Supply (AGR)
  •  Industrial Service Supply (IND)
  • Groundwater Recharge (GWR)
  • Freshwater Replenishment (FRSH)
  • Water Contact Recreation (REC-1)
  • Non-Contact Water Recreation (REC-2)
  • Navigation (NAV)
  • Commercial and Sport fishing (COMM)
  • Cold Freshwater Habitat (COLD)
  • Wildlife Habitat (WILD)
  • Warm Freshwater Habitat (WARM)
  • Migration of Aquatic Organisms (MIGR)
  • Spawning, Reproduction and Development (SPWN)

Available Documents