Many of the world’s lakes lie within temperate regions and experience seasonal ice cover. However, climate change is reducing the extent and duration of ice cover in many systems. Despite increasing interest in winter limnology, we have very little knowledge of vertical distributions of phytoplankton and primary productivity under lake ice. We know even less about the composition and dynamics of sympagic (ice-associated) algal communities. Using modified bottle assays and custom-made sympagic enclosures, we investigated algal community structure and primary productivity patterns under snow-covered and cleared ice in several North American lakes spanning gradients of size, trophic status, and organic content. We also spectrally characterized light penetration through ice and under-ice water columns. Snow and ice cover influenced not only the quantity but also the quality (spectral signature) of light entering the water column. Despite altered light climates, primary productivity was surprisingly high, with maximal rates immediately under snow-covered ice in eutrophic systems approaching 60% of summertime values (~1200mg C · m-3 · d-1). Under-ice phytoplankton communities were dominated by representatives of genera considered to be "understory" or low-light adapted genera during the open water season, while the sympagic community was dominated by filamentous centric diatoms.