Lake Invaders

The quagga mussel has made a mess of Lake Mead. Is Lake Tahoe its next victim?

The quagga mussel is about half the size of your fingernail. It originates from the Caspian Sea, but in recent times its shells have been irritating the feet of beachgoers on the shores of Lake Michigan. It filters vital nutrients from freshwater, disturbs the food chain, endangers fisheries, excretes carbon, spurs algae growth and clouds the water. Other than that, it’s great.

In 2007, the mussel was found in Lake Mead—presumably spread via the bottom of some pleasure boat that once plied the Great Lakes—and has made itself at home there, with 50,000 specimens per square meter in some areas of the lake. It has also been found throughout the lower Colorado River basin. Now it may be making its way toward the deep blue waters of Lake Tahoe, the 11th deepest lake in the world.

When boat inspectors found 37 quagga mussels attached to a powerboat at 7,000-foot Spooner Summit on Aug. 7, it increased the threat that a biological invasion of a damaging aquatic species could be in Northern Nevada’s future. The mussels have also been detected at Lahontan and Rye Patch reservoirs, within 150 miles of Lake Tahoe.

“You are adding a new and voracious predator to the system,” says Todd Tietjen, a limnology specialist with the Southern Nevada Water Authority. “I can say it has the potential to ruin the fishery and make the lake less attractive. Lake Tahoe is known for its crystal-clear waters. Your top selling point would be diminished.”

The mussels are active breeders that attach themselves not only to the bottoms of boats, but also water-intake pipes and screens, creating an infrastructure nightmare for water systems. Costs reached more than $500 million annually to control the mussels at power plants, water systems and on boats and docks in the Great Lakes, according to Mark Hoddle of the Center for Invasive Species Research at the University of California, Riverside. The Army Corps of Engineers estimated in 2009 that the species, if established, could cost $22 million to the Lake Tahoe region.

“It’s unpredictable,” says Sudeep Chandra, an associate professor of limnology and conservation ecology at the University of Nevada, Reno. “This is the entire problem with biological invasions. If mussels establish in Lake Tahoe, then the worst-case scenarios are what our colleagues have observed back east, where they have to replace water pipes, treat the sewer systems and things like that. They attach to the water-intake pipes and they grow on the inside. It’s a pretty amazing sight to see.”

In order to protect Lake Tahoe, a mandatory Watercraft Inspection Program is in place in the summer at roadside stations such as Spooner Summit, about 8 miles from the lake. From October to April, inspections and decontaminations take place at lakeside locations such as Cave Rock and Sand Harbor State Park. Meanwhile, Lake Mead boaters are being asked to clean, drain and dry their vessels before bringing them north.

“No one wants [the quagga mussel invasion] to evolve on Lake Tahoe itself,” says Kent Turner, the National Park Service’s resource management chief for Lake Mead. “A pound of prevention is worth a million dollars of cure.”

It’s unclear whether the mussels would take to Lake Tahoe as they have to Lake Mead. For one thing, they need calcium to grow shells and eventually spawn—and, while there’s plenty of calcium in Lake Mead, there’s not nearly as much in Lake Tahoe. The colder water temperatures at Tahoe’s 6,225-foot elevation may also impede quagga mussel growth.

“This is the reason we’re trying to do some of these tests now,” says Chandra of scientific studies that began in November, with the first results to be available by July. “Can these things survive, and how fast would they grow if they did survive? And at what stages would they be limited or not?”

In 2009, the researchers found in a preliminary study that Lake Tahoe conditions may indeed be conducive to mussel concentration. “We ended up taking adults from Lake Mead, feeding them for 50 days with low-calcium Lake Tahoe water,” Chandra says. “What we ended up finding is that most of them exhibited positive growth and 86 percent of them survived. This is an indication to us that they are able to survive there in the short term.”