The dataset contains CO2 efflux, hydraulic and water chemistry data from six field sites which vary in location, size and catchment characteristics. Measurements were made at: i) two sites in the UK - the River Kelvin (335 km2, semi-urban catchment) and Drumtee water (9.6 km2, peat dominated catchment); ii) four sites in the Peruvian Amazon - Main Trail (5 km2, seasonally active stream in a rainforest catchment), New Colpita stream (7 km2, perennial stream in a rainforest catchment), La Torre river (2000 km2, rainforest catchment) and Tambopata river (14 000 km2, rainforest catchment with some small scale agriculture and gold mining). CO2 efflux was measured at all sites on each sampling occasion alongside a range of other parameters to enable investigation into the controls on CO2 efflux. Parameters measured include flow velocity and water depth (from which other hydraulic parameters can be calculated), DIC concentration and pH (from which pCO2 can be calculated) and water temperature. Sampling was carried out over several years, thus capturing a range of seasons and flow conditions, and at all sites, measurement locations were chosen to ensure that a range of flow intensities were included.