Divers help study spread of non-native plants in Tahoe
November 29, 2005
The invasive weed Eurasian watermilfoil has infested more of Emerald Bay’s waters than originally thought, according to the California State Lands Commission.
“This may be a bigger problem than anyone ever realized,” Steve Jenkins, assistant chief of State Lands’ division of environmental planning and management, said earlier this month.
Milfoil and a new non-native plant, the curly leaf pondweed, have infested at least two acres of water off Ski Run Boulevard, according to Kim Melody, who works on invasive weed program for the Tahoe Resource Conservation District.
The tall, dark plant chokes off oxygen to fish, encourages algae growth, and smothers native aquatic plants, according to experts. It can also affect swimmers and boaters by clogging waterways. A common aquarium plant, milfoil is believed to have arrived in Lake Tahoe 30 years ago and has been found in the Truckee River and at least 16 locations in the lake.
Melody has designed Tahoe’s first sign for marinas warning boaters they may help spread the weed if they don’t take certain precautions.
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State Lands surveyed Emerald Bay last week to see if a removal project in May was successful.
What they found gave them food for thought.
While milfoil did not regrow in areas addressed in May, divers found a much larger area infested with the plant in the rest of the bay.
State Lands is responsible for leasing and managing public lands on the bed of Lake Tahoe below an elevation of 6,223 feet.
Volunteer divers with Tahoe Divers Conservancy also gathered at Ski Run Boulevard last week to learn how to identify the weed so they can help remove it by hand. Other methods, like machine harvesting, help spread milfoil because it can reproduce through fragments alone.
Divers have been noticing milfoil is spreading and increasing in the lake for a decade now, said Phil Catarino, the conservancy’s president.
“Everyone is working on the lake, but there’s not anyone sticking their head in the water,” Catarino said.
Clean Water Act
Jenkins believes not doing anything about milfoil’s spread is a violation of Lake Tahoe’s unique status under the Clean Water Act as an Outstanding National Resource Water. The status prohibits longterm degradation to the lake, including biological degradation.
“From our standpoint,” Jenkins said, “it interferes with recreational boating, and recreational use of the lake, should the infestation continue to advance.”
In Tahoe’s land of many rules, there are no regulations regarding milfoil or boat cleaning. Melody’s milfoil sign is the first step in a long-awaited public outreach program.
“It’s just starting the awareness,” Melody said. “It’s so easily spread in the right conditions that we are likely to lose a lot of ecological function in our shallow areas and beaches.”
Many experts believe the source of milfoil is the Tahoe Keys, where almost all 150 acres of its canals are infested with the weed. Boats may pick it up on their rotors on their way out to the lake, and the Keys’ practice of mowing it also allows fragments of the plants to float into the lake and start colonies elsewhere, said Jenkins and several other experts.
State Lands has no jurisdiction in Tahoe Keys, Jenkins said.
Nutrients help growth
In Lake Tahoe, milfoil can get the sunlight it needs at depths of 20 feet. An influx of nutrients into the lake is also a culprit in its growth.
There’s already focus on reducing nutrients in Lake Tahoe because they encourage algae growth and cause the lake to lose clarity.
Lahontan Water Board, which regulates water quality at Lake Tahoe, believes reducing nutrients is the best long-term solution to controlling milfoil.
Division manager Lauri Kemper said an alarm was raised 10 years ago that milfoil would spread fast through Lake Tahoe, but it never happened. “I’m not aware of any evidence that things are getting unmanageable,” she said.
The Tahoe Regional Planning Agency is just beginning to be more proactive on milfoil and other invasive weeds, and is looking into expanding public education, said spokeswoman Julie Regan..
While Lahontan has ruled out herbicide as a last resort, TRPA is becoming more open to it.
“We are not outruling herbicide,” Regan said. “With technology, there may be ways to use something like that if it’s done properly.”