Understanding Water Movement in Lake Tahoe
Water movement shapes everything in Lake Tahoe — from where nutrients travel, to how oxygen reaches the deepest waters, to how quickly pollutants or invasive species can spread. Measuring currents at a single point tells only part of the story. To protect the lake, we must understand how water moves across the entire basin, from surface to depth and from shore to shore.
UC Davis TERC uses a combination of innovative field experiments, long-term monitoring, and advanced instrumentation to build that comprehensive picture.
Following the Currents: Drifter Studies
To track basin-wide circulation, TERC deploys surface drifters equipped with underwater drogues (sails) that allow them to move solely with the currents. Each drifter contains a GPS unit, and newer versions transmit real-time data via satellite.
These studies have revealed that Lake Tahoe’s circulation is dominated by two major gyres:
- A counterclockwise gyre in the north
- A clockwise gyre in the south
Smaller, wind-driven gyres form and dissipate along the lake’s edges, especially nearshore. Drifter research first showed that invasive species such as Asian clams could potentially travel from the east to the west shore in less than a day — highlighting how quickly biological or chemical pollutants can spread once introduced.
Current collaborations, including work with students from the Tahoe Expedition Academy, are expanding monitoring along the north shore and developing tools to visualize current patterns in real time.
Spring Upwelling: Winds That Reshape the Lake
In late spring, strong wind events can trigger upwelling, a process that brings cold, nutrient-rich deep water to the surface. These events typically occur from late May to mid-June, when the lake is weakly stratified, and winds are strong.
Upwelling can:
- Deliver nutrients to surface waters, potentially fueling algal growth
- Transport oxygen-rich surface water to depth
- Rapidly redistribute heat and particles along the shoreline
In spring 2018, TERC scientists led a large-scale experiment deploying over half a million dollars’ worth of instruments along a half-mile transect offshore. The array measured currents, temperature, oxygen, and clarity, while water samples were collected weekly for nutrient and particle analyses.
These experiments help researchers understand how wind-driven events influence water quality and ecosystem dynamics — and how those processes may shift under a warming climate.
Computational Fluid Dynamics - Modeling
Deepwater Monitoring: Oxygen and the Future of the Lake
Near the deepest part of Lake Tahoe, a vertical array of 20 temperature sensors and a dissolved oxygen sensor continuously records conditions from near the surface to the lake bottom. Every 30 minutes, measurements are logged, generating nearly 1 million data points every 6 months.
Dissolved oxygen is one of the most critical indicators of lake health. The rate at which deep waters lose oxygen determines whether “dead zones” could form in the future. Whether that occurs depends on how effectively the lake mixes — a process strongly influenced by temperature, wind, and climate.
These long-term data allow scientists to refine models that predict:
- How mixing processes transport oxygen to depth
- How quickly microbial processes consume oxygen
- How climate change may alter stratification and deepwater renewal
Why Water Movement Matters
From surface currents to wind-driven upwelling to deepwater mixing, physical dynamics determine how Lake Tahoe functions. They control the transport of nutrients, the spread of invasive species, the distribution of heat, and the oxygen supply to the lake’s depths.
By combining drifters, large-scale experiments, and continuous deepwater monitoring, TERC is building one of the most detailed physical records of any alpine lake. This integrated understanding is essential for predicting how Lake Tahoe will respond to climate change — and for protecting its clarity, ecosystems, and communities for generations to come.
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