Dreissenid Mussel Infestations In California: A Comprehensive Overview.pdf

A Comprehensive Overview (September 2011)

## Introduction

Quagga and zebra mussel infestations have been a growing concern in California since their initial detection in Lake Havasu (San Bernardino County) and the Colorado River Aqueduct in early 2007. Since then, these invasive dreissenid mussels have spread to numerous waterbodies in Southern California, primarily through raw water supplies from the Colorado River. This report summarizes known infestations, monitoring efforts, response plans, and water quality data for affected waterbodies across various counties.

## Waterbody Summaries by Water District

### Metropolitan Water District of Southern California (MWD)

MWD serves over 19 million customers in Los Angeles, Orange, San Diego, Riverside, San Bernardino, and Ventura Counties. They manage nine reservoirs, three of which are infested with quagga mussels: Copper Basin, Lake Mathews, and Lake Skinner. MWD employs chlorine disinfection at specific points within the Colorado River Aqueduct to prevent mussel spread.

MWD has developed a comprehensive Quagga Mussel Control Plan, including a boat inspection program for Diamond Valley Lake and Lake Skinner. The plan categorizes waterbodies into three groups based on their potential impact on downstream locations and outlines actions for Category III (non-contiguous, uninfested) waterbodies to prevent mussel introduction. They have submitted numerous Raw Water Discharge Plans to the California Department of Fish and Game (DFG), all focusing on minimizing mussel spread during routine maintenance activities and legal water releases.

## Infested Waterbodies and Response Strategies

| Waterbody Name | County | Infestation Date | Monitoring/Response Plan |
| --- | --- | --- | --- |
| Lake Havasu | San Bernardino | January 2007 | N/A |
| Colorado River Aqueduct | Riverside | July 2007 | N/A |
| Lake Mathews | Riverside | August 2007 | N/A |
| Lake Skinner | Riverside | August 2007 | N/A |
| Lower Otay Reservoir, San Vicente Reservoir, Murray Reservoir, etc. (Multiple Counties) | San Diego | August-September 2007 | Various monitoring programs and response plans submitted to DFG |
| El Capitan Reservoir, Sweetwater Reservoir, Dixon Lake, etc. (Multiple Counties) | San Diego | December 2007 - January 2008 | Individual response plans for each waterbody |
| Kraemer Basin, Anaheim Lake, Irvine Lake, etc. (Orange County) | Orange | September 2009 - May 2010 | Multiple monitoring and control plans submitted to DFG |

## Key Points

- As of January 2008, San Justo Reservoir in San Benito County is the only known location with a zebra mussel infestation in California.
- MWD has implemented robust measures to prevent further spread, including chlorine disinfection and detailed discharge plans.
- Over ten Raw Water Discharge Plans have been approved by DFG for MWD, ensuring responsible water management practices.
- Various water districts and counties have submitted monitoring and response plans tailored to their specific infested waterbodies.