The dataset includes a collection of Critical Thermal maxima values (CTmax) for 676 Serratella ignita and 155 Baetis rhodani specimens, sampled in 4 Scottish lakes in 2016 and 2017. The dataset indicates date of collection for each specimen, location, and body size. 

Larval sampling took place within a circle of 5 m radius from the loggers, using a standard kick sampling net through kick netting method.  Samples were collected on up to three dates at each site. Once collected, larvae were placed in tanks filled with river water and immediately transported to the laboratory (average trip 2h by car). CT_max values were established in experiments using high performance Grant Optima TX150 circulating water baths with programmable heating settings. Larvae were always handled using plastic spoons, to prevent damage. They were placed in 8 plastic cups (7x15 cm), one for each location. Additional plastic cups were used if the number of individuals exceeded 30. Cups were filled with respective site water in order to preserve thermal conditions and minimise physiological stress. The cups were then placed in the water bath. Prior to experiments, all individuals were equilibrated at 10°C for 10 minutes. During each thermal trial, samples were subjected to a constant water temperature increase of 0.1°C/minute, which was monitored and controlled by Grant TX150 programmable circulating water bath with C2G cooling attachment (Grant Instruments, Shepreth, UK). CT_max values for each individual were recorded when no physical response occurred after three consecutive prods (Becker & Genoway, 1979); these individuals were then removed from cups while the remaining individuals continued to be monitored. All the CTmax experiments were performed on the day of sample collection.

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