Lake Tahoe report suggests historic rise in algae and surging microplastics are reasons to take action

UC Davis' annual State of the Lake report on the health of Lake Tahoe has found massive changes since last year. 

Among them include a “collapse” of zooplankton, a dramatic rise in algae, which zooplankton eat; and a corresponding decline in the lake’s clarity. Murkier lake waters make it harder for ultraviolet rays to reach life below the surface that thrives on it. These issues also affect Lake Tahoe’s renowned blue hue.

Tahoe Environmental Research Center Director Geoffrey Schladow “any one of these changes would be a big deal in a single year.” 

“All three occurring at once is particularly alarming and a huge opportunity to learn lessons that can be used to inform future management,” he wrote in the report.

The report also indicates there's a major human-caused problem: microplastic contamination.

“Most of the microplastics come from carelessness of all of us, in our use of plastic and how we dispose of it,” Schladow said.

He says if Tahoe residents and tourists want to make a difference, then “using less plastic and making sure you take it home with you, dispose of it properly, will make an impact.

The rapid algae growth is an increase of six-fold in the past 50 years, and it is now at the highest level since the lake's been studied.  

Schladow says the effects of algae begin at the water's edge.

“That's where people interact with the lake and there are slimy rocks and there are algae washing up on the shores,” he said.

But the algae also affects water clarity — and that's a problem that goes beyond appearances.

“The clarity of the lake allows UV radiation to penetrate.  And that's one of the largest factors that controls invasive species in the lake,” Schladow added.

The new report also found that a different type of algae has become the most dominant type. And, tellingly, it's a species that thrives in the high nitrogen levels found in wildfire smoke.

Other key findings from the study include:

• “fine particle concentrations, which greatly impact clarity, were the highest on record” in 2021, which also could be due to wildfires
• “Climate change is evident in nearly all the long-term meteorological trends, including rising air temperatures and a declining snowpack.” June and July were the warmest since scientists began the annual lake reporter in 2010. And 2021 was the third-driest year on record.
• Tahoe’s mysis shrimp populations are declining, but they likely will return, and researchers want to learn more about how this will affect Tahoe clarity and zooplankton in future years.