Data file contains bore hole temperature measurements for Uomullyakh and Polar Fox lagoons carried out in April 2017 as well as porewater conductivity measurements carried out in the Laboratory. GeoPrecision temperature chains (accuracy of 0.1 °C and a resolution of 0.01 °C) remained in the borehole for 5 days at Polar Fox Lagoon and 11 days at Uomullyakh Lagoon. To account for drilling heat effects, the observed temperature drift for each thermistor was analysed following Lachenbruch (1982). For the calculation of freezing points the electrical conductivity of the porewater (referenced to 25 °C) was converted to molality (mol/kg) using the TEOS package in MATLAB (McDougall and Barker, 2010).