Invasive weeds, non-native fish threaten Tahoe waters

An unnatural, man-made environment at Lake Tahoe's Keys has become the breeding ground for not only out-of-control invasive plant life, but for undesirable bottom-feeding fish, officials at a workshop said last week.

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Eurasian water milfoil and curlyleaf pondweed received most of the attention at Thursday's workshop on Lake Tahoe's aquatic invasive species, with a new look at how these plants provide habitat for newly introduced fish.
Invasive plants cover about 250 acres of Lake Tahoe's underwater area, with roughly 160 acres concentrated in the Tahoe Keys, according to 2006 data provided by Lars Anderson, lead scientist with the U.S. Department of Agriculture's Exotic and Invasive Weed Research Group.
Left alone, dense stands of milfoil and pondweed shade out native species, clog boat motors, discourage water sports and may encourage algae growth by pumping phosphorus into the lake, according to researchers.
Milfoil has been documented in the Keys since the late 1980s and has spread as far as Incline Village, taking root in more than 20 locations around the lake, including a large swath in Emerald Bay.

Recreational boating is the most common way for these plants to spread between lakes, when they become entangled in boats and their trailers. Fragments can live for weeks in moist boat engines before finding a suitable place to root.

In addition to being an invasive species itself, milfoil provides suitable habitat for Lake Tahoe's most recent aquatic invaders, warm-water fish, according to Sudeep Chandra, a limnologist at the University of Nevada, Reno.

Largemouth bass, smallmouth bass, black crappie, catfish, bluegill and goldfish have all taken up residence in the lake within the past decade. In addition to the habitat provided by milfoil, these species have been able to survive in Lake Tahoe because of the relatively warm water in sheltered marinas, according to U.S. Forest Service literature.

"We have a plant problem coupled with a fish problem," said Chandra. "The good news is these are early invaders."

While Chandra said there have been preliminary observations of bass on the East Shore, the spread of warm-water, bottom-feeding fish should be easier to control than their plant counterparts because of their recent arrival.

The Tahoe Regional Planning Agency and the Tahoe Divers Conservancy will continue diver-assisted vacuum removal of milfoil and pondweed around the lake this summer, with a focus on Emerald Bay.

Recent invasions of Western waters by quagga mussels have added urgency to the debate surrounding the management of Lake Tahoe's non-native species. However, coordinating the basin's natural resource agencies quickly enough to stop the creatures in case of an infestation may be the real challenge.

"I don't have confidence in the fact that Tahoe is not at risk," said Jeff Herod, program coordinator for the U.S. Fish and Wildlife Service California-Nevada Operations Aquatic Nuisance Species program, at a workshop presented last week on the aquatic invasive species threat posed to Lake Tahoe. The workshop was attended by scientists, public agency officials, private businesses and members of the public.

Quagga mussels were discovered in Lake Mead on Jan. 6, but Herod said they've likely been there for three or four years because of the sizes of the shells found.

Out of 780 interviews of boaters, conducted over the past two summers by Marion Wittman, a Ph.D. candidate at the University of California, Santa Barbara, 265 came to Lake Tahoe after trips to bodies of water containing invasive species.

Nearly a dozen of these boaters came to Tahoe after previous visits to Lake Mead, Lake Havasu and the Colorado River drainage. All have established populations of quagga mussels, according to Wittman.

Quagga mussels can quickly coat underwater surfaces, damaging boats and piers and clogging water intakes to municipal water supplies.

Much of the debate at Thursday's workshop centered around whether one agency should take the lead in the prevention of quagga mussel infestation, or if it could be effectively prevented by the coordinated efforts of basin agencies.

"Somebody has to step in, and you know who that's going to be," said John Singlaub, executive director for the Tahoe Regional Planning Agency. "We've got a challenge ahead of us and we're willing to step in, but it's not a simple problem."

Over the next month Singlaub pledged to examine the creation of a aquatic non-native species coordinator position with Pam Wilcox, administrator of Nevada Division of State Lands, and Harold Singer, executive officer of the Lahontan Regional Water Quality Control Board.

The position would be "the key first step to get this moving," according to Singlaub. He added feasibility studies and funding options would be critical for the long-term protection of Lake Tahoe from invasive species, but knew there was an immediacy required because of these species

"We've got to get moving on this now," Singlaub said.

Tahoe Resource Conservation District will be hosting a public watercraft inspection and decontamination training on May 15 from 10 a.m. to 1 p.m. at Tahoe Keys Marina. More information on the workshop is available by contacting Jenny Francis at (530) 543-1501, ext. 109.

Lars Anderson, lead scientist with the United States Department of Agriculture's Exotic and Invasive Weed Research Group, saw Thursday's collaboration as a positive first step.

"What I'm seeing happening is really remarkable," Anderson said. "Momentum just has to be sustained."

Non-native species

a plant or animal deliberately or accidentally introduced into a new habitat.



Invasive species

a species whose introduction does or is likely to cause economic or environmental harm or harm to human health.

- Source: U.S. Environmental Protection Agency