This notice regards:
Why It Matters To You
Golden mussels pose a direct threat to Westlands farmers by clogging pumps, pipelines, sand media filters, drip systems, and turnout structures. Once established, mussels are nearly impossible to remove without major system disruption. Preventive action is the most effective and lowest‑cost protection for irrigation reliability and farm productivity.
What Steps Is The District Taking
Westlands is working to develop a layered strategy of targeted treatments, preventative cleaning and dewatering, and site specific filtration methods to minimize the effects of the Golden Mussel on our ability to deliver timely, reliable, and affordable water to our growers. As an initial measure, staff coordinated with a planned fall silt removal project to include concurrent removal of Golden Mussel within those facilities. Westlands is actively engaging with state and federal partners in a coordinated effort to manage and control the Golden Mussel within the Central Valley Project facilities
How They Spread Into Westlands
Golden mussels release microscopic larvae (veligers) that can remain suspended in water for up to 30 days. These veligers travel from the Delta waters through CVP pumping plants, O’Neill Forebay, San Luis Reservoir, and ultimately into Westlands turnouts.
Mussels also spread through equipment movement when pumps, hoses, pipes, or tanks retain even small amounts of water. Never move equipment containing water or algae growth between ranches or fields. Follow recommended Clean-Drain-Dry and/or Hot Water Flushing as described below.
How To Deal With Golden Mussels
Clean – Drain – Dry
CLEAN: Remove debris, algae, and mud from pumps, hoses, filters, and tanks. Most effective when used in conjunction with hot-water flushing.
DRAIN: Empty all water from equipment and pipelines before moving them.
DRY: Allow 7–14 days of drying time, or use a hot‑water flush if equipment must be moved sooner.
Hot‑Water Flushing (Highly Effective)
Flush irrigation systems using 140–145°F water for a minimum of 10 seconds of contact time. To protect pipe material vulnerable to higher temperatures, extend flushing for at least 60 seconds at a minimum of 125°F.
Applicable to:
- Pipes and tanks
- Pumps and controls
- Valves and fittings
- Filters and housings
This method is organic‑compliant and one of the most reliable ways to kill mussels and veligers when temperatures are achieved throughout the system.
Filtration & Screens
Proper filtration is a critical first line of defense.
Sand Media Filters:
- Backwash sand media filters regularly to prevent clogging and media channeling
- Monitor pressure loss across filters
- Replace media when pressure loss increases or water quality declines
Screens and Strainers
- Inspect Intake screens weekly
- Clean immediately if debris or biofouling is observed
- Screens are beneficial to exclude adult mussels upstream of sand media filters
Filtration is especially important at surface water groundwater recharge sites to prevent mussels and biofouling from entering wells.
Filtration Guidance by Golden Mussel Life Stage*
| Target Life Stage | Typical Size | Control Objective | Recommended Filtration/ Exclusion Method | Key Design & Maintenance Notes |
|---|---|---|---|---|
| Larval (Veliger & Early Juvenile) | ~0.07–10 mm | Prevent larvae and newly settled juveniles from entering irrigation systems | Sand Media Filtration • Media #20 (mean filtration 0.06–0.08 mm) • Media #30 (mean filtration .038 mm) | Current data suggests this is effective method for larval interception • Requires regular backwashing to prevent channeling • Monitor pressure loss closely • Replace media as needed |
| Adult Mussels | ~2–3 cm (¾–1¼ in) | Exclude adults before they enter pipelines, pumps, or filters | Screens and Strainers (Primary Control) • Installed at intakes, turnouts, and pump inlets | • Screens must be inspected weekly • Clean immediately if fouling is observed |
*Consult your irrigation design professional for any changes in media to evaluate effect on pump and irrigation system design and performance.
On‑Farm Monitoring
Watch for sudden pressure loss, reduced emitter flow, increased backwash frequency, unusual pump behavior, or visible mussels on screens and pump bowls. Report concerns to Westlands Water District Operations (559) 884-2523.
Additional Control Methods (Testing and Evaluation Ongoing)
Chlorine: Chlorine has been used in other invasive mussel control programs. Application rates should be site specific and under the guidance of an Irrigation Specialist and a registered Pest Control Advisor.
Ozone: Effective oxidant for headworks systems; no residue.
UV: 254nm used for other invasive mussels and should be effective on Golden Mussel veligers; requires clear water to be effective.
Copper/Potassium Compounds: Effective with extended exposure times. Application rates should be site specific and under the guidance of an Irrigation Specialist and a registered Pest Control Advisor.
Useful Reference Information
Temperature Limits:
- PVC – 140°F (short exposure)
- HDPE – 160°F
- Rubber – 140°F
- Steel – 200°F+
Chemical Compatibility:
- PVC – Moderate with chlorine; low ozone resistance
- HDPE – High chlorine resistance; moderate ozone resistance
- EPDM – Low resistance to chlorine/ozone
- Stainless Steel – High compatibility with all treatments
Reporting & Help
Report suspected mussels immediately to Westlands Water District Customer Accounting (559) 224-1523 or Field Engineering (559) 884-2523 Departments . Coordinate with CDFW if needed.
Bottom Line For Farmers
Golden mussels threaten water deliveries, crop yields, and irrigation infrastructure. Clean–Drain–Dry, hot‑water flushing, filtration upkeep, and regular monitoring are the strongest preventive tools available. Every farmer plays a vital role in protecting Westlands’ water supply.
*Contact Westlands Staff for the most recent evolving guidance and recommendations. Updates will be provided at monthly Board meetings and Growers Notices
No. 796