As surface sea temperatures rise, our waters are becoming a more inviting environment for certain bacteria. Vibrio are naturally occurring bacteria found in marine and brackish environments; while most are harmless, some species pose potential health risks to humans.

These pathogens can cause infections by seafood consumption or by direct exposure when we swim in coastal waters. The Vibrio group of pathogens prefers warmer water, creating growing concerns as climate change accelerates warming patterns. This isn’t good news for those of us who love swimming in the sea. Environments that we thought previously safe could become a health risk in the coming years.

How can we better understand the effects of warmer sea temperatures and develop strategies to protect human health? Researchers from Deltares, the Dutch knowledge institute for applied research, are studying the impact of climate change on Vibrio bacteria in Lake Grevelingen in the Netherlands.

Why this matters

Warmer waters create ideal conditions for harmful Vibrio bacteria to thrive. Franco Forlano from Deltares explains the public health implications.

We believe that environmental changes caused by the climate can increase the risks of illness caused by certain types of Vibrio bacteria. This is due to warmer temperatures and heavier rainfall events during summer time. This creates scenarios where we increase our exposure – when it is warm we tend to go to swimming areas on the coast and eat more seafood – and simultaneously increases the abundance of these potential pathogens.

The research aimed to:

1. Identify the environmental factors that shape the distribution of Vibrio pathogens, while also assessing the molecular detection techniques
2. Develop an environmental suitability model for Vibrio species that will better support local authorities in shaping public health strategies and monitoring protocols

Lead researcher Franco Forlano (in the video above), said: “I went many times on holiday to the beach with friends and family. We spent time there, played games or had dinner at sunset. I think that these nice experiences are an extra motivation for me to help keep these landscapes safe for the enjoyment of others in the coming years.”

Key findings

Temperature is the primary driver of Vibrio bacteria growth. Here’s a snapshot of what the research revealed:

1. Vibrio concentrations increased significantly as water temperature rose, peaking in summer (August).
2. Pathogens concentrate in shallower, warmer nearshore waters – precisely where swimmers and beach users are most exposed.
3. Sediment harbours twice as much Vibrio as water, indicating less-studied contamination pathways
4. Lake Grevelingen’s naturally high salinity acts as a buffer against optimal pathogen growth.
5. Currently, the lake is relatively low risk; but climate events like heatwaves or heavy rainfall could destabilise conditions.

How did we complete the research?

The team monitored water and sediment samples for 16 months (May 2023 to October 2024) at five designated bathing locations in Lake Grevelingen, the largest brackish lake in western Europe. The lake’s conditions made it ideal for this study: it experiences seasonal temperature swings from 13 °C in winter to 22 °C in summer, supports both recreational use and shellfish aquaculture and has previously tested positive for Vibrio species, including cholera.

The team measured the abundance of Vibrio and compared it to different environmental factors, aiming to establish the optimal conditions that increase abundance. To do this, they tested modern molecular techniques with the goal of speeding up the detection of these risks during regular monitoring.

A module with Vibrio growth ranges was added into a pre-existing model of Lake Grevelingen, showing us the times where growth conditions for these pathogens was optimal.

Recommendations for protection

1. A critical gap remains: current predictive models rely heavily on North American data. Expanding monitoring and data collection across European water will create more accurate, locally relevant tools to protect public health.
2. Monitoring should include sediment samples since these can contain high levels of Vibrio.
3. Rather than expensive year-round surveillance, the researchers recommend reactive, threshold-based monitoring triggered by:

• Sustained high water temperatures or heatwave events
• Heavy rainfall that could alter the salinity conditions