Underwater lake heatwaves threatening aquatic life

Lakes are essential to ecosystems, providing freshwater, supporting biodiversity and offering crucial habitat for fish and other aquatic species.

- IESTYN WOOLWAY

But a recent study shows that lakes around the world are warming, not just at the surface, but deep below as well. Subsurface heatwaves in lakes, defined as extreme periods of high water temperature below the surface, are increasing in frequency, duration and intensity.

These hidden extremes could have serious consequences for lake ecosystems. Despite that, the issue remains largely unmonitored and poorly understood.

Lake heatwaves are similar to those in the atmosphere or ocean. They are prolonged periods of excessive warmth. Most research to date has focused on surface temperatures, where climate change has already caused more frequent and intense heatwaves over recent decades.

These surface events can disrupt the chemical and physical balance of lakes, damage food webs and, in some cases, cause mass fish die-offs.

Aquatic species respond to surface heatwaves in different ways. Some benefit if the warming expands their preferred temperature range. But many others, particularly those already living near their thermal limits, face significant stress.

In lakes that stratify during summer—where warm surface water sits above a cooler bottom layer—some species seek refuge from the heat by migrating to deeper water. But what happens when that deeper refuge is no longer cool?