Read the pdf file: Golden.Mussels.Update.03.19.26.Final

Dear Water Users:

In late December 2025, the District notified its Water Users and others about the presence of golden mussels throughout the District’s Distribution System. Staff were directed by the Board to take immediate actions to surround the topic and eradicate the invasive species as soon as possible.

On February 10, the Board approved a Staff-recommended, two-phase approach to mitigate golden mussels involving copper-based treatment.  The first phase (March 2026) is an aggressive system-wide treatment to achieve maximum mortality of the mussels.  The second phase is to establish a long-term management plan to treat incoming golden mussel larvae (veligers) at the District’s two surface water import locations and any residual adult mussels throughout the District as well as a robust monitoring program for frequent inspections.

On March 9, Phase One treatment began consisting of treating the entire District system with Natrix CA at 1 ppm of copper. Phase One is anticipated to last for up to 28 days (around April 6).  According to the Natrix CA label, on which the District has relied to develop Phase One, the 1 ppm copper treatment is safe for crops. This is an emergency action being taken by the District.  Water Users should independently verify compatibility with their own facilities (including any aluminum piping or components) and promptly notify the District of any concerns.  Also, Water Users may notice dead mussels in their filtration systems.  For purpose of tracking treatment efficacy, please notify the District IMMEDIATELY if you discover dead or alive golden mussels in your irrigation systems.  See above picture for example of what has already been seen.

Golden mussels attach to pipes/structures and can build upon each other, which greatly reduce pipeline capacity, starve pumps, clog trash racks including traveling water screens, with the most vulnerable being small diameter pipelines.

Assistance from Water Users may be necessary to move treated water into the most downstream facilities to reach all parts of the system.