Randomly distributed patches of smooth surfaces are readily observed on most water bodies. They are called natural slicks when biogenic surfactants in the surface microlayer accumulate above a certain threshold. Slicks typically form under low wind conditions (< 6 m s-1), having spatial scales from tens of meters to kilometers. They suppress the formation of wind-induced Gravity-Capillary Waves (GCW), leading to altered surface reflectance of light and microwaves, and can also affect near-surface convective motions. Therefore, it is of interest to understand how slicks affect the air-water exchange of momentum, heat, and gas, which can influence the biogeochemical dynamics in the near-surface layer of lakes and oceans. We examined the spatiotemporal variability of momentum flux caused by slicks in Lake Geneva using eddy covariance instrument setups mounted on an autonomous catamaran during several field campaigns. These measurements were combined with aerial and shore-based imagery (both RGB and thermal). We also sampled surface microlayers in an accompanying boat to determine whether visually-identified smooth patches had higher concentrations of fluorescent dissolved organic matter, a proxy for natural surfactants. Using wavelet analysis, we investigated short-time O(1 min) averaged air-water momentum flux variations associated with the transition from smooth slicks to rough surface areas, which could not be captured by conventional eddy covariance analysis. Results suggest that under light wind conditions and in the absence of short GCW, wind stress cannot effectively be transferred to the water, leading to a reduction of momentum exchange within slicks in comparison to the surrounding non-slick areas. The resulting slick-induced horizontal gradients in vertical mixing can contribute to spatial variability in surface temperature and near-surface heat content, which in turn affects air-water exchange processes.