Lake Tahoe is known for its mesmerizing clear, blue water. But there are multiple threats to the lake that may someday change the color and worse, downgrade the quality of the water.
Some of the most difficult of these threats to address are invasive species, specifically two types of aquatic plants that are not native and are moving from an area of the lake known as the Tahoe Keys into Lake Tahoe itself.
The plants are Eurasian watermilfoil and curly-leaf pondweed.
Invasive aquatic species at Lake Tahoe/Tahoe Keys Property Owners Association
“The ecology of Lake Tahoe is actually incredibly complex. So the plants don’t just grow and do nothing. They actually alter the entire ecosystem of the lake,” said Jesse Patterson, chief strategy officer of the League to Save Lake Tahoe.
Patterson explained that the plants actually suck nutrients from the soil and sediment of the lake, bringing them into the water where algae can use them to bloom.
Algae blooms aren't necessarily a bad thing. Algae is part of the lake's ecosystem, Patterson said, but because of climate change, the lake is getting warmer and blooms are becoming larger and more frequent.
“Now, with the water getting warmer, and nutrients being pulled up into the water by these invasive weeds, it's kind of the perfect storm to get hazardous algae blooms, which are the real concern, which is when it can affect people or pets,” he said.
The problem with the Tahoe Keys is that they're a man-made series of lagoons and canals on 172 acres in the southern tip of the California side of the lake. It is connected to the lake through two main channels.
That has made the area "ground zero" for invasive species, Patterson said.
“Sounded like a good idea in the 50s and then in the 60s when it was built, but it turns out Mother Nature had other ideas,” he said.
The area's shallow, warmer waters combined with the natural marshes nutrients have been a perfect place for invasive species, especially aquatic plants to grow and thrive.
Water in the Tahoe Keys filled with weeds/Tahoe Keys Property Owners Association
Lake Tahoe has an advantage over other lakes. Its waters are naturally deeper and colder, which has kept species out, Patterson said. However, as the warming climate warms the waters of the lake, those species are finding their way out of the lagoons and into the lake.
Patterson said his group and other conservation groups are trying to get at the source of the problem.
“We want to address the source so we don’t have to keep putting Band-Aids on the little infestations around the lake but actually address the source, get to the root of the problem and keep Tahoe blue for future generations,” he said.
With that being said, Patterson said the effort to stop the spread of the weeds needs to be deliberate for several reasons.
For one thing, the plants are very well established in some places and are resilient. In addition, something that worked in one place may not work in an ecosystem as unique as Lake Tahoe.
“We need to find this best set of practices and the best way to do this safely is to test them in a controlled way where you can see not only how effective they are at treating the plants but what other things they may effect,” he said.
One way to eradicate invasive plant species is UV light. Light panels are put onto the bottom of a large boat. The boat then floats over the areas where the plants are established.
Patterson said the light essentially gives the plants a sunburn, bursting their cell walls killing them.
The technology has been used successfully in some marinas in the lake, but the water in the Keys is murkier than the rest of the lake and there are more plants there.
They still plan on trying it there to see if works.
Another possible solution is targeted herbicide, but the Clean Waters Act establishes special protections for Lake Tahoe. Herbicides that have been used for decades in other lakes have never been used there.
Patterson said his group is now on the long and winding road of navigating the restrictions on the lake to see if it is possible to test those herbicides in a very small and targeted way.
“This challenge in front of us, this Tahoe Keys issue, is one where we believe it’s worth doing a test, a very controlled test,” he said.
They want to use the herbicides in combination with other elimination methods.
A method that was installed in 2018 that doesn't introduce chemicals or high-tech boats, but has, so far, proved very effective is bubble curtains.
“Just think of a wall of bubbles from the ground all the way to the top," Patterson said, "Allows boats to pass through, but with the plant fragments, which is how they spread, can’t make it past the wall and they’re actually contained inside and you can scoop them out.”
A bubble curtain as seen from a drone/League to Save Lake Tahoe
The League to Save Lake Tahoe worked with property owners in the Tahoe Keys to put in the curtain at one of the channels connecting the lagoons to the open lake.
It was so successful there, that another was put in at the second channel and in some marinas around the lake as well. Patterson is hopeful those bubble curtains will help stop the spread of the weeds.
There is an urgency to the invasive species problem at Lake Tahoe, he said. The lake is getting warmer and warmer, faster and faster, which means if something is not done quickly the once sparkling blue jewel of the Sierra Nevada will instead be chocked green.
“Once you’ve changed the ecology, and you have this complex food and nutrient system working out of sight, that blue lake can go green very quickly,” he said.
There are things visitors to the lake can do to help, Patterson said. When visiting, he suggested people download an app that allows them to alert lake management when they see an invasive species.
“That’s really the best way is to learn about it, keep your eyes open, which can be hard to do because it’s so pretty up here, but keep an eye out and that’s how we’re going to get a handle on this is everyone doing a little bit of their part to enjoy Lake Tahoe and keep Tahoe blue,” he said.
Jesse Patterson, Chief Strategy Officer, League to Save Lake Tahoe