Beavers are starting to colonize low arctic tundra regions in Alaska and Canada, which hasimplications for surface water changes and ice-rich permafrost degradation. In this study, weassessed the spatial and temporal dynamics of beaver dam building in relation to surface waterdynamics and thermokarst landforms using sub-meter resolution satellite imagery acquiredbetween 2002 and 2019 for two tundra areas in northwestern Alaska. In a 100 km2study area nearKotzebue, the number of dams increased markedly from 2 to 98 between 2002 and 2019. In a430 km2study area encompassing the entire northern Baldwin Peninsula, the number of damsincreased from 94 to 409 between 2010 and 2019, indicating a regional trend. Correlating data onbeaver dam numbers with surface water area mapped for 12 individual years between 2002 and2019 for the Kotzebue study area showed a significant positive correlation (R2=0.61; p < .003).Beaver-influenced waterbodies accounted for two-thirds of the 8.3% increase in total surface waterareain the Kotzebue study area during the 17 year period. Beavers specifically targeted thermokarstlandforms in their dam building activities. Flooding of drained thermokarst lake basins accountedfor 68% of beaver-influenced surface water increases, damming of lake outlets accounted for 26%,and damming of beaded streams accounted for 6%. Surface water increases resulting from beaverdam building likely exacerbated permafrost degradation in the region, but dam failure alsofactored into the drainage of several thermokarst lakes in the northern Baldwin Peninsula studyregion, which could promote local permafrost aggradation in freshly exposed lake sediments. Ourfindings highlight that beaver-driven ecosystem engineering must be carefully considered whenaccounting for changes occurring in some permafrost regions, and in particular, regional surfacewater dynamics in low Arctic and Boreal landscapes.