No larger than a thumbnail or pistachio nuts, zebra, quagga and golden mussels hardly appear formidable. 

But what they lack in size, the freshwater relatives of clams and oysters make up for in their ability to rapidly reproduce and spread.

For native ecosystems, water managers and recreationalists, they are diminutive nightmares. And with recent nearby discoveries, they pose growing threats to Nevada’s waterways.

Aquatic invasive mussels damage infrastructure by attaching to surfaces using a cementlike adhesive they secrete from their body, potentially accumulating in what officials describe as “catastrophic densities.” They can clog drinking water supply lines, harm hydroelectric generation facilities and irrigation systems and cause millions of dollars in damages.

There is no known safe way to eradicate them once they get established. 

Originating overseas — quagga and zebra mussels are from Eastern Europe, and golden mussels come from China — they are transported by water, or equipment such as boats that were in infected water. 

Quagga mussels, known as the “evil cousin” of zebra mussels, already exist in Lake Mead.

But in late 2024, golden mussels were found in a California waterway. It was the first time the species had been found in the United States, and they’ve since spread throughout central and Southern California. And last month, Colorado River officials for the first time discovered invasive zebra mussels in the upper river.

Nevada waterways are currently free of zebra and golden mussels. But, Nevada officials and water managers are preparing for what it could mean if the zebra or golden mussels find their way into Lake Mead and other state water bodies and using their experience with quagga mussels as a baseline. 

Research shows that if quagga and zebra mussels are found in the same area, quagga dominate zebra mussels, according to Southern Nevada Water Authority (SNWA) Regional Water Quality Manager Todd Tietjen. Research also shows that golden mussels could outperform both of them, “which is why we are really ramping up our detection efforts.” 

Water managers are conducting public outreach to raise awareness about properly cleaning, draining and drying watercraft to prevent the spread of mussels, but it’s going to be hard to stop their proliferation, said Kevin Netcher, aquatic invasive species coordinator at the Nevada Department of Wildlife (NDOW): “That’s more concerning to the West.”

‘An ongoing nuisance’ 

While golden mussels were just discovered for the first time last year, zebra and quagga mussels were first reported in the northeastern United States in the 1980s. They’ve since made their way across the country, reproducing at exponential rates.

Golden mussels can broadcast spawn year round, producing millions of offspring, and quagga mussels can grow in the thousands per square meter, making it nearly impossible to control infestations once they are established, according to Sudeep Chandra, limnology professor and director of the Global Water Center at UNR, who has incubated quagga mussels with water from lakes such as Tahoe, Pyramid and Truckee to assess their potential to establish in various water bodies.

Quagga mussels were first found at Lake Mead National Recreation Area in 2007, although the population was likely established several years before it was discovered. 

“They’re an ongoing nuisance,” Tietjen said. “They’re one of the many things we monitor in the lake for overall health.”

But, because of a slower growth rate in Lake Mead than in more nutrient-rich water bodies, combined with the size of the tunnels SNWA uses to pull water from Lake Mead — intake three measures 24 feet in diameter — the overall risk to the authority’s infrastructure is low, Tietjen said. 

“It’s not zero, but it’s sort of manageable and monitorable,” he said. “It’s almost inconceivable they would ever close that pipe down.” 

But that doesn’t mean they aren’t damaging the ecosystem and infrastructure. They now grow on everything from duct tape to rope to steel, and continuous treatment is required to keep the mussels’ numbers at bay. They have also spread throughout the lower Colorado River system.

Left unchecked, the mussels can cause millions of dollars in damages.

Data from the National Oceanic and Atmospheric Administration shows that between 1989 and 2004, quagga mussels had an estimated cumulative economic impact of $267 million nationwide at drinking water treatment plants and electric generation facilities.

That number has continued to grow — more recent estimates pinpoint about $500 million spent annually in the Great Lakes area alone to combat invasive mussels, and another $500 million spent annually in California.

The Bureau of Reclamation spends approximately $1 million annually on quagga mussel control at Hoover Dam, and SNWA budgets more than $500,000 annually for quagga mussel control activities.

NDOW spends roughly $1.5 million on the prevention of aquatic invasive species, with half of that money directed solely at Lake Mead, according to Netcher. 

Prevention rather than eradication

Between Oct. 1, 2023, and Sept. 30, 2024, more than 13,700 boats were inspected after exiting Lake Mead and Lake Mohave, a reservoir on the Colorado River near Laughlin. Nearly 650 were contaminated with aquatic invasive species or showed visible signs of being high risk.

“At Lake Mead, we see it every day,” Netcher said. “We decontaminate a lot of boats.”

All Western states conduct DNA monitoring for quagga and zebra mussels, and now golden mussels, at uninfested water bodies, Netcher said. In Nevada, all major reservoirs are sampled at least twice a year. 

SNWA, which pulls almost all its water — about 90 percent — from Lake Mead via submerged pipes, is also establishing a methodology to monitor for the presence of mussel DNA.

The authority uses a chloramine treatment (a disinfectant that meets Environmental Protection Agency standards and is safe to drink, but that the authority removes during its treatment process) to limit quagga infestations. The chloramine, which irritates the mussels so that they stop swimming, sink and are captured in filters, is added in the intake process, so that it never enters the lake.

The authority expects that to work if other invasive mussels make their way into the lake, spokesperson Bronson Mack said in an email. 

“Based on research, we anticipate that the current preventive treatment for quaggas colonization within Lake Mead infrastructure will be effective for zebra mussels, and we’ll continue to evaluate that going forward,” he wrote.

There currently is no way to eradicate aquatic invasive species on a large scale, Chandra said, which is why it’s so important to have policies and programs in place to minimize their transfer between locations.

Educational programs to combat invasive species are a good step but not enough, Chandra said. Instead, it’s critical that federal, state, regional and local governments develop uniform policies that minimize the establishment and spread of new invasive species.

“A little bit of prevention can go a long way in preventing long-lasting impact,” he wrote in an email.

Netcher echoed that sentiment, saying that in Nevada, the goal remains prevention rather than eradication. Reservoirs such as Lake Mead are too large, and any chemical application would kill off substantial numbers of other species. 

“We’re always going to have them,” he said.  

Golden mussels an even larger threat 

While it's nearly impossible to stop the downstream spread of zebra mussels, golden mussels are a different story, Netcher said. Because their populations are currently isolated to California waterways they can only reach Nevada through overland transport. 

Originating in China, golden mussels are similar in appearance and are as harmful as quagga and zebra mussels, with a catch — they can establish themselves in water with more diverse temperature and salinity ranges. They’ve since established themselves throughout central and Southern California waterways and associated infrastructure, and there’s little the state has been able to do to slow their spread.

Golden mussels don’t just spread via boats — they cling to almost anything in contact with infected water, including toys, life jackets, shoes and fishing gear. They can also survive more than a week without water.

In May, a Lake Tahoe boat inspection station intercepted golden mussels on a boat bound for the lake.

“That close call is a warning,” reported the League to Save Lake Tahoe. “Golden mussels are not a distant threat.”

Netcher agrees.

“Since they’re in the water systems, they’re actively spreading right now,” Netcher said. “It’s going to be very challenging to prevent the spread of that species.”