Milfoil malaise: State Lands becomes first agency to proactively fight the weed
Lake Tahoe has been invaded.
Phalanxes of a tall, dark green weed called Eurasian water milfoil are choking off oxygen to fish, encouraging algae growth, and smothering native aquatic plants in at least 16 locations in Lake Tahoe, including Emerald Bay and the Truckee River.
Legend has it that 30 years ago, a boy moving from the Tahoe Keys dumped the contents of his aquarium into the lagoon, including a sprig of milfoil. It’s more likely milfoil hitched a ride on the back of a boat.
The Tahoe Keys, encompassing more than 150 acres, are nearly 100 percent infested with the non-native plant today.
Eurasian milfoil has been here for at least 30 years, experts say, yet no agency has taken proactive steps to address the weed’s existence or reduce its spread until this year.
In May, the California State Lands Commission took a dive team to Emerald Bay and pulled up 60 pounds of the mucky plant by its roots. Organizers hope the pilot project will show whether hand-removal is an effective method to control the plants.
State Lands will return in October to assess their progress and remove remaining plants.
Called suction removal, the method is considered the safest way to address the problem. It’s also one of the most expensive: the four-day project costs about $10,000.
State Lands is responsible for leasing and managing public lands. It manages the bed of Lake Tahoe below an elevation of 6,223 feet.
Eurasian milfoil can grow to heights of five feet. In Lake Tahoe, it can get the sunlight it needs at depths of 20 feet. An influx of nutrients into Lake Tahoe is also a culprit in its growth.
Some have wondered why the state lands commission – an agency that does not have an environmental protection or regulatory role – had to take the lead on this pernicious plant.
“It’s been a longtime coming and a good example of what an agency can do if they set their mind to it,” said Lars Andersen, a lead scientist with the U.S. Department of Agriculture’s invasive research unit based at UC Davis. He helped monitor the State Lands project in May.
“TRPA and Lahontan should look at this problem and very carefully examine their own responsibilities in keeping exotic species out of the lake,” Andersen said.
“Our role isn’t to be an implementer of projects, but rather to facilitate those projects like the project in Emerald Bay,” said Angela Moniot, spokeswoman for the TRPA.
To date, there are no posted signs at the marinas and no preventive or public outreach program to address the invasive weed problem.
“I was shocked to find that at the access areas at Lake Tahoe there are no signs saying this lake is infested with milfoil, clean your boat and trailer,” said Holly Crosson, who worked for nearly two decades as manager of Vermont’s milfoil control program. She’s now a scientist with UC Davis, also working to reduce the spread of non-native aquatic plants.
“In Vermont, we were very proactive about spread prevention,” she said.
The Lahontan Regional Water Quality Control Board is charged with making sure Tahoe’s water meets standards for safe drinking and fish health.
While recognizing it’s annoying for marinas and an impact on the ecosystem, a division manager at Lahontan said they have no problem with milfoil from a water quality standpoint.
“We haven’t seen any data that tells us it’s causing a water quality concern,” said Lauri Kemper, division manager at Lahontan.
TRPA has proposed boat washing stations for getting rid of exotic plants before they enter the water. That proposal must still be approved by its governing board and implemented.
Scientists said boat washing stations are needed. While milfoil is already established, there’s a host of invasive aquatic weeds waiting a ride to Tahoe. An invasive pondweed was discovered this year.
“Even though you’ve already got the milfoil in there, there’s worse ones on the way,” said Marty Hilovsky, an aquatic biologist and president of EnviroScience. The company has reduced Eurasian milfoil in 80 lakes in the eastern U.S. using the milfoil weevil, a bug native to North America that feeds solely on milfoil, both native and non-native varieties.
“Anything the community can do to keep the invasive species out of there will be well worth it,” Hilovsky said.
But boat washing stations do not address the infestation already in the water. Once established, milfoil is nearly impossible to get rid of, scientists said.
Both TRPA and Lahontan have rejected proposals to use herbicides to control the weed, Andersen said.
That doesn’t leave many options for the owners of the Tahoe Keys Marina, who two years ago paid $15,000 to transport air pumps called Solar Bees for a trial run. The pumps haven’t worked, said Dick Horton, a marina owner, and he’s now willing to try anything.
“I’m happy to look at anything that might work,” Horton said. “It’s about as bad as it can get.”
For now, the marina has been mowing the weed to enable boat traffic to move freely.
Mowing is the worst option, Crosson said, because pieces of milfoil will root and reestablish on their own.
“It’s a known fact that mechanical harvesting spreads the plant,” said Crosson.
The Keys plants are chopped before they can ever flower or seed, but its pieces float out into the lake after it’s mowed. Wherever those pieces land is another infestation waiting to happen.
Charles Goldman, who has researched Lake Tahoe’s waters for 46 years, and who first pointed out development was having an affect on its famed clarity, is in favor of using herbicide to rid the Keys of its infestation. Andersen and Crosson also agreed it would be the best option.
Modern herbicides are plant specific and breakdown quickly in the water, Goldman said. The benefit to the lake would far outweigh any detrimental effects.
Lahontan will not budge on the herbicide issue.
“We want them to exhaust all other options before putting a chemical into the water of Lake Tahoe,” said Kemper, division manager at Lahontan.