Polar deserts are characterized by limited water availability across much of the terrestrial landscape. In the McMurdo Dry Valleys, Antarctica, soil active layers are wetted only briefly after infrequent snowfall (<10 cm yr−1). Adjacent to glacial meltwater streams and lakes, however, sediments and soils appear visibly wetted throughout the summer. We hypothesized that this apparent wicking of water from aquatic environments is controlled by capillary action determined by the physical properties of near-shore sediments including slope, particle size distribution, and depth to permafrost. We performed synoptic sampling of near-shore sediments around two lakes in Taylor Valley, East Antarctica. We measured the water content, active layer depth, particle size distribution, and topography to determine the relative importance of shore slope, pore size distribution, and depth of the active layer on the spatial dimension of wetted hydrologic margins. The horizontal dimension (distance from the lake edge) of wetted margins (HW) and slopes ranged from 1.1 to 32.9 m and 1 to 61% and active layer depth ranged from 5.5 to >120 cm. Our results indicate that particle size distributions of near-shore sediments are homogeneous; slope had a greater effect on the dimensions of wetted margins, explaining 73% of the variance in HW. These findings show that the spatial dimensions of wetted zones are controlled by a suite of physical parameters that may be easily measured using remotely sensed data and a limited number of samples. Such information is useful for constraining landscape-scale models of nutrient redistribution because intermittently wetted soils are zones of enhanced biogeochemical transformation and transport in desert ecosystems.