This dataset includes continuous data on water temperature, dissolved oxygen, conductivity, and photosynthetically active radiation (PAR) from low-order streams and main-stem rivers in Northwestern Alaska. Water temperatures were determined using a HOBO Water Temp Pro v2 (Onset Computer Corporation, Bourne, MA, USA) with ±0.2 °C accuracy. Dissolved oxygen was measured using HOBO U26 Dissolved Oxygen logger (Onset Computer Corporation, Bourne, MA, USA) with an accuracy of ± 0.2 mg/L up to 8 mg/L; ± 0.5 mg/L from 8 to 20 mg/L. Conductivity was measured with HOBO U24-001 freshwater conductivity data logger (Onset Computer Corporation, Bourne, MA, USA) with an accuracy of ± 3%. Photosynthetically active radiation was measured with a HOBO UA-002-64 Pendant Temperature/Light 64K Data Logger (Onset Computer Corporation, Bourne, MA, USA). Sensors were placed at several locations within each stream as well as in the main river below the tributary junction in order to assess stream thermal state. All sensor types were also placed in impoundments from beaver (Castor canadensis) dams on rivers and in small lakes.