New boating requirements and temporary upper division reservoir closures will protect District water

It’s making headlines these days: the invasion of a little bivalve – the golden mussel -- that is spreading through California waterways and posing a significant threat to water infrastructure, recreation, ecosystems and water quality. Because the mussels reproduce so fast, they can quickly clog pipes and machinery, affecting drinking water plants and power facility operations, as well as harming local ecosystems by outcompeting native species. 

As a result, water district officials across Northern California are temporarily shutting down reservoirs or requiring quarantines of boats in effort to keep this invasive species in check.

Fortunately, the mussels have not been found in any of the Nevada Irrigation District’s (NID) reservoirs, and the District has taken proactive measures to prevent any intrusion.   

The new protocols: before launching into NID’s foothill reservoirs of Rollins and Scotts Flat, all motorized watercrafts must be quarantined for a minimum of 30 days or undergo hot-water decontamination performed by an authorized entity. In the upper elevations of the Sierra Nevada, NID’s boat launches at Jackson Meadows and Bowman reservoirs will be closed until further notice for the summer season. Jackson Meadows and Bowman reservoirs are the only upper elevation NID lakes that allow motorized boats.

The preventive focus is on motorized boats, the primary vector for the spread: “Golden mussels can be transferred between reservoirs by boats, their trailers and equipment, especially when not properly cleaned, drained, and dried before moving to a new body of water,” says NID Director of Recreation Monica Reyes.   

NID began its quarantine program in March, and since then more than 800 boaters have been tagged for a 30 or 60-day countdown to when they can launch. Other agencies have also new protocols, including at Lake Berryessa, Lake Tahoe, and Folsom Lake.

 Golden Mussel 101: All That Glitters Isn’t Good

Golden mussels (Limnoperna fortunei) are native to China and Southeast Asia. In October 2024, golden mussels were found by California Department of Water Resources (DWR) staff at the Port of Stockton, some 110 miles southeast of Grass Valley. The mussels likely infiltrated California by a ship traveling from an international port, according to DWR at the time.

It was the first detection of the species in North America, and the finding immediately sparked an alarm. The port is located in the Sacramento-San Joaquin Delta, the West Coast’s largest and exceptionally fragile tidal estuary, as well as the primary hub for the state’s water exports through the State Water Project that provides water to more than 750,000 acres of farmland and 27 million people.

In the first several months of 2025, the mussels have spread and been found as larvae and adults in about 30 areas around the central and southern Delta.

Golden mussels, named for their yellow-brown color, are bivalves with two hinged shells. Fully grown, they typically are less than two inches in length and grow in dense clumps or colonies. They can live about three years.

There are four primary characteristics that make golden mussels incredibly invasive:

• Free-swimming larvae – Larval mussels swim in the water column for the first month of their life. Because they are free swimming and extremely small, they can be drawn into engines, ballast tanks, live wells and bilges, and be easily transported from one body of water to the next.
• Byssal threads – zebra, quagga and golden mussels have byssal threads that allow them to attach to any stable substrate in the water including rocks, plants, fiberglass, plastic, cement, steel, and even onto other mussels.
• Rapid reproduction rate – golden mussels have a very rapid reproduction rate, spawning year-round (if conditions permit), where one single female can produce up to one million eggs in a year.
• Filter feeders – Feeding on plankton (the foundation of the aquatic food chain). It has been observed that a mussel can filter up to a liter in a day.  

Stronger, Faster, Hungrier: The Golden Mussel Threat

For years, the aquatic invasive focus has been on quagga and zebra mussels (dreissenid mussels), which are also invasive species that can do great damage. Boaters and reservoir managers have done a great job at keeping quagga/zebra from our waters, however the golden mussel is posing a greater threat.

There are three important and relevant ways the golden mussel is a greater threat to NID’s infrastructure and water conveyance systems:  

First, golden mussels are adaptable. They are able to thrive in both freshwater and brackish water environments. This elevates the vector from the Delta to our foothill and mountain reservoirs.

Second is the ability to thrive in low calcium water bodies. Golden mussels can complete their lifecycle in water bodies with low calcium levels, ranging from 1-50 milligrams per liter (mg/L).  Scotts Flat has calcium concentrations ranging from 2.95 mg/L to 3.74 mg/L, and Rollins calcium ranges from 4.31 mg/L to 7.33 mg/L. At higher elevations, Bowman ranges from 3.40 mg/L to 4.54 mg/L, and Jackson Meadows ranges from 3.37 mg/L to 4.09 mg/L.  

Third is the ability to live in varying water temperatures. Golden mussels can tolerate a wide range of temperatures, from 5 - 35°C (41 - 95°F). Scotts Flat’s temperature ranges from 7.29°C to 29.92°C (45 - 85°F), and Rollins is from 6.97°C to 28.74°C (44 - 83°F). Bowman temperature ranges from 15.25°C to 23.47°C (61 - 74°F) and Jackson Meadows ranges from 17.06°C to 22.79°C (62 - 73°F).  

NID is taking proactive and necessary steps to keep the Golden Mussel from being introduced to District systems. The cost of doing nothing is too great.

Eradicating mussels from larger bodies of water is nearly impossible. In localized cases, mussels can be manually removed from water bodies by costly scraping and suctioning. In large water systems, this can be a futile effort in trying to remove large colonies.

Eradicating the mussel utilizing chemical control methods have been tested with mixed results. Chemicals may not be suitable for many situations, and adding the compounds into a water supply could have numerous unintended environmental impacts. 

Finally, the cost of applying control methods to larger-scale projects, like treating entire water bodies, can cost millions. For example, in Brazil, which has seen an extensive breakout of golden mussels that now is impacting 40 percent of the nation’s hydropower plants, the estimated annual cost of monitoring and maintenance ranges from $6.9 million to $8 million, with an additional $120 million in lost revenue. 

NID’s Launches Boat Seal Program at Scotts Flat and Rollins Reservoirs

Through the Watercraft Inspection Database (WID), boat traffic can be monitored. Owners of any trailered or motorized watercraft wishing to launch at either Scotts Flat or Rollins reservoirs must check in with NID on-site staff to receive a quarantine seal and be entered into the WID database.

NID staff will attach a red quarantine seal, which must remain for 30 days and cannot be launched in any other waterbody during the quarantine period. Boats with ballasts, bilges or livewells will have a 60-day quarantine.

Vessels that have finished the quarantine may then launch at Rollins or Scotts Flat reservoirs. Upon exit from the reservoir, all watercraft must have a blue re-entry seal attached by NID staff to be allowed to return and freely launch at either Rollins or Scotts Flat. If a boat does not get a blue re-entry seal, it will be required to undergo another quarantine period or decontamination.

Any watercraft wishing to launch sooner than the required quarantine period must have a hot-water decontamination performed by an authorized entity at Lake Tahoe or Lake Berryessa. Vessels are allowed to launch immediately following decontamination.  

Will NID accept a quarantine started at another reservoir?

Through the WID database, information is available to track boat inspections, decontaminations, seal applications and removals. Because of this, NID will accept red quarantine seals from other agencies’ reservoirs, as long as the following criteria are met:

• The 30/60-day red quarantine seal from another agency has been added to the WID database. Please keep in mind NID does require a 60-day quarantine on all watercrafts with ballast, bilge or livewells, not all lakes require this.
• Decontamination certificates only from Lake Berryessa or Lake Tahoe.
• The lake attaching the seal from has not tested positive for quagga, zebra or golden mussels.

Watch a short video on how the NID boat seal program works. “Invasion of the Bivalves: Protecting NID from Golden Mussels” (4:17 minutes)

Apart from the boat seal programs at Rollins and Scotts Flat, NID has closed its boat launches at Jackson Meadows and Bowman reservoirs in the Sierra Nevada for the 2025 season until further notice. Jackson Meadows and Bowman reservoirs are the only NID upper division lakes that allow motorized boats.

“Jackson Meadows and Bowman are high in the Sierra, and they are the headwaters of the District’s water delivery system. Because that is the top of our water network, if golden mussels were introduced there, they could be invade our entire system, which would be devastating,” Reyes says.