A project observing the climate change impact on streams and rivers in Wales has seen its average temperature rise 1C (1.8F) in the past 40 years.
The Llyn Brianne Observatory has been collecting data for four decades on the streams around the River Tywi that flow into the Carmarthenshire reservoir.
Prof Steve Ormerod and his wife Isabelle Durance run the study.
He said they were “pretty sure” the climate change effect has led to a year-on-year fall in insect numbers.
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