In August 1988, researchers released green and red dyes into a Canadian lake to uncover its hidden circulation; wind at the surface was driving water in different directions below

In August 1988, scientists carried out an unusual experiment in Twin West Lake, about 75 kilometres east of Vancouver, Canada, to investigate how wind influences water movement inside a seemingly still lake. By releasing brightly coloured dyes into the water and tracking their movement, researchers were able to make otherwise invisible currents visible.

The findings, later published in Limnology and Oceanography, showed that wind did not simply push the lake's upper water in one direction. Instead, it helped generate a layered circulation, with water near the surface moving with the wind while water farther down in the same upper layer travelled in the opposite direction.

A small lake with a hidden structure

Twin West Lake sits at an elevation of roughly 500 metres and is a small, oligotrophic lake, meaning it has relatively low nutrient concentrations. During summer, the lake becomes strongly stratified.


A warm upper layer, known as the epilimnion, sits above a much colder lower layer called the hypolimnion. Separating them is a narrow transition zone known as the thermocline, which in this lake was only about three metres below the surface.

That structure was crucial to the experiment. Although the lake might appear relatively calm from above, its water could be moving in different directions at different depths.

Green and red dyes become underwater tracers

Researchers released the dyes into Twin West Lake on August 2, 18 and 24, 1988. Sodium fluorescein, which appeared green, was released near the centre of the lake, while Rhodamine WT, which appeared red, was released from the shoreline.

For each release, researchers slowly poured about two litres of a 20% dye solution into the water. Because the concentrated solution was initially slightly denser than the surrounding lake water, it first sank. As it mixed with the lake water and became diluted, however, the thermocline restricted its downward movement and helped keep the tracer within the upper layer.

The dyes effectively turned invisible currents into something researchers could see and measure.

Cameras tracked the coloured water

The experiment relied on more than simply watching the dye spread. Researchers photographed and videotaped the coloured patches from a vantage point overlooking the lake. A camera captured images every two minutes, while instruments positioned at the lake's centre recorded wind speed and direction.

Fourteen marker buoys arranged on a 60-metre grid provided fixed reference points. By comparing the position and shape of the dye clouds against those markers, researchers could reconstruct how the coloured water moved through the lake over time. This allowed them to examine not only where the dye travelled, but also how its movement changed with depth within the stratified upper layer.

The clearest result came on August 24

The August 24 experiment produced the clearest evidence of the lake's layered circulation. According to the Limnology and Oceanography study, the central green dye responded to wind-driven circulation, but its movement varied significantly with depth. Near the surface, the dye plume travelled in the same direction as the wind at an average speed of about 2.8 centimetres per second.

Farther down in the epilimnion, however, the water carried the dye in the opposite direction at approximately 1 centimetre per second. The result was striking because the wind was not simply dragging the entire upper layer of water along with it. Instead, the observations indicated a circulation in which water moved with the wind near the surface and returned in the opposite direction below.

As the wind changed direction, the dye cloud stretched and became distorted, providing further evidence that different parts of the upper layer were moving differently. The researchers concluded that horizontal spreading was influenced by differences in water velocity with depth, changes in wind direction and turbulent mixing.

What the dye revealed about lake circulation

The coloured patches were not merely a visual demonstration. By processing the video images, researchers could measure how quickly the dye clouds expanded and estimate the rate at which material dispersed horizontally through the lake.

This type of tracer experiment is useful because substances released into a lake rarely remain exactly where they were introduced. Nutrients, pollutants and other dissolved materials can be carried by currents and redistributed through turbulence and mixing.

Understanding that movement is important for applications ranging from pollution studies to lake management. A substance released at one location may travel considerably farther than expected depending on the lake's circulation, wind conditions and internal layering.

Other tracer studies have demonstrated similar effects. Research published in Water Resources Research, for example, used Rhodamine WT in a stratified lake and found that boundary mixing produced a distinct dye intrusion that travelled more than 200 metres offshore. The study also recorded elevated eddy diffusivity near the lake boundary, illustrating how circulation and mixing can strongly influence the transport of dissolved material.

Making invisible currents visible

Modern tracer experiments use considerably more sophisticated equipment, but the basic idea remains much the same.

In one study published in the Journal of Environmental Engineering, researchers introduced Rhodamine WT into an arm of California's Keswick Reservoir and monitored the tracer for four days using moored water-quality sondes. They combined those measurements with surface drifters and the Delft3D hydrodynamic model to investigate how the dye moved through the reservoir.

The measurements showed water velocities of roughly 1–5 centimetres per second across much of the study area, while the model helped researchers examine how mixing developed as the dyed water travelled downstream.

The technology was far more advanced than the equipment available during the Twin West Lake experiment in 1988. But the principle was essentially unchanged: introduce a tracer, follow where it goes and use its movement to reveal currents that cannot otherwise be seen.

At Twin West Lake, that simple approach exposed something easy to miss from the shoreline. The lake did not have one uniform surface current carrying water in a single direction. Instead, wind helped produce a layered circulation, with surface water moving one way and deeper water within the epilimnion moving back the other way.

For a lake that appeared quiet from above, the dye showed just how dynamic the water beneath the surface could actually be.