6We monitored temperatures in stream water, groundwater and riparian wetland surface 7 water over 18 months in a 3.2 km 2 moorland catchment in the Scottish Highlands. The 8 stream occupies a glaciated valley, aligned west-east and has three main headwater 9 tributaries with northerly, southerly and westerly aspects. Much of the stream network is 10 fringed by riparian peatlands. Stream temperatures are mainly regulated by energy 11 exchanges at the air-water interface. However, they are also influenced by inflows from the 12 saturated riparian zone, where surface water source areas are strongly connected with the 13 stream network. Consequently, the spatial distribution of stream temperatures exhibits 14 limited variability. However, there are significant summer differences between the 15 headwaters, despite their close proximity to each other. This is consistent with aspect (and 16 incident radiation), with the south and west facing headwaters having higher temperatures. 17The largest, north-facing sub-catchment shows lower summer diurnal temperature 18 variability, suggesting that lower radiation inputs dampen temperature extremes. Whilst 19 stream water temperature regimes in the lower catchment exhibit little change along a 1km 20 reach, they are similar to those in the largest headwater; probably reflecting size and 21 comparable catchment aspect and hydrological flow paths. Our results suggest that 22