Rising summer air temperatures are placing significant stress on the delicate ecosystem of the UK Rivers. Baseline monitoring revealed concerning peak instream temperatures, frequently exceeding 20°C and even reaching 21°C during heatwaves. This warming trend posed a direct threat to the resident brown trout population (Salmo trutta), a keystone species for UK river’s health and a source of enjoyment for local anglers. Elevated water temperatures reduce dissolved oxygen levels, increase metabolic stress on fish, and can even lead to mortality. The lack of sufficient shade along stretches of the river exacerbated this issue, allowing direct sunlight to heat the water.  

The Solution: Nature-Based Climate Resilience

Recognising the critical role of riparian vegetation in regulating stream temperatures, The Woodland Trust created the Keeping Rivers Cool partnership initiative and created a habitat restoration project focused on increasing tree canopy cover, assisted by the Environment Agency in England, Rivers and Fisheries Trusts of Scotland and Natural Resources Wales, among other agencies.

The core strategy involved:

Strategic Riparian Planting: Planting native tree species along the riverbanks to create shade over the water. Careful consideration was given to species selection to maximize shade provision while enhancing biodiversity and bank stability.

Long-Term Temperature Monitoring: To quantify the impact of the increased canopy cover, the team deployed Tinytag Aquatic 2 data loggers at multiple points along the river, both in open and shaded sections. These robust and waterproof loggers provided accurate and continuous instream temperature readings and were a good low cost option to collect river temperatures to build up a detailed record over the whole year and in different conditions.

Why Tinytag Aquatic 2?

The Tinytag Aquatic 2 data loggers were chosen as they were a reliable low cost temperature logger that would be easily deployed and recovered later to download the data.

Implementation and Monitoring:

Over the following years, the project teams meticulously planted native trees and expanded the riparian buffer zone along targeted sections of UK rivers. Simultaneously, the Tinytag Aquatic 2 loggers continuously recorded instream temperatures, capturing daily and seasonal fluctuations. Additional sensors were added to collect external air temperature and solar irradiance sensor data were also collected to establish and identify correlations as the riparian canopy expanded. Aquaread Water quality sensors were added to collect pH, ORP, Conductivity, TDS, SSG, Resistivity, Salinity, Dissolved Oxygen and Temperature readings.

The Results: A Measurable Difference

The long-term data collected by the Tinytag Aquatic 2 loggers provided compelling evidence of the positive impact of increased tree canopy and the Aquaread sensors were able to show how the canopy shaded area and improved water quality for wildlife:

Significant Temperature Reduction: In the years following significant canopy development, peak summer instream temperatures in the shaded sections of the river consistently registered 2-3°C lower than in unshaded control sections. On exceptionally hot days where unshaded areas reached 20-21°C, shaded areas peaked at a much more favourable 17-18°C.

Reduced Temperature Range: The daily temperature fluctuations were also less extreme in shaded areas, creating a more stable and less stressful environment for aquatic life. Lower temperatures improved the water quality and dissolved oxygen levels.

Correlation with Canopy Cover: Analysis of the data clearly demonstrated a strong inverse correlation between the density of the overhead canopy and peak instream temperatures.

Positive Impact on wildlife: Anecdotal evidence and observational surveys indicated a healthier and more abundant brown trout population in the shaded stretches of the river. Local anglers reported increased catches and observed more active fish, directly linking the cooler water temperatures to improved fish welfare.

“For years, we’ve worried about the river getting too warm in the summer. Since the trees have grown and provided more shade, the difference is noticeable. The water feels cooler, and I’ve definitely seen more trout in those areas. It’s fantastic to see the river thriving again!” – Local Angler

Conclusion: A Win-Win for Ecology and Community

This project successfully demonstrated the powerful and cost-effective role of natural solutions, like riparian tree planting, in mitigating the impacts of rising temperatures on freshwater ecosystems. The precise and reliable data provided by the sensor were crucial in quantifying the benefits of increased canopy cover, showcasing a clear reduction in peak instream temperatures and a positive response from native species.

For more information on the Tinytag Aquatic 2 data logger, please visit: https://www.omniinstruments.co.uk/p/tinytag-aquatic-underwater-temperature-loggers/

For more information on the River Condition Monitoring, please visit: https://www.omniinstruments.co.uk/c/water-quality-waste-water-management-systems/water-quality-meters/

To learn more about the river restoration project, you can download the Keeping Rivers Cool: Guidance Manual.

Details on the Temperature, Dissolved Oxygen, or any other river monitoring conditions, please contact us.