A Novel Approach to High Resolution Three‐Dimensional Temperature Measurements in Rivers and Streams

Water temperature is a crucial factor determining aquatic habitat characteristics and biological community structure. Despite its high relevance, conventional methods to measure thermal heterogeneity in surface waters are strongly limited in their spatial representativeness. Specifically, there is a lack of spatially three‐dimensional methods capable of in situ characterization of water temperatures at high resolution for entire lotic waterbodies. This study presents an innovative prototype device which fulfils these requirements. We tested the device and method in a 400‐m‐long river stretch and compared the results with thermal heterogeneity mapping based on thermal infrared remote sensing. Our prototype device collected 6306 temperature measurements within 1 h throughout the river stretch, encompassing all habitat types with varying river morphology. Comparison with thermal infrared remote sensing revealed significant discrepancies, challenging the accuracy and representativeness of currently used methods that only record surface water temperatures. The observed substantial differences between surface and bottom temperatures of up to 9.36°C underscore the importance of measurements that include both near‐bottom and near‐surface measurements of high spatial resolution. The unprecedented quantity of temperature data points derived from the novel approach presented herein, coupled with the precise positional and depth information, opens new opportunities for a representative assessment of thermal heterogeneity in aquatic habitats.