Hydrologic inferences drawn from the sedimentary record in large, glacier-fed, lakes require careful understanding of the sediment cascade in the contributing watershed and lake basin. As sediment sources are exposed by retreating glaciers, and as new sediment storage sites emerge, the nature of lacustrine sedimentary proxy of extreme hydrologic events changes. Two large glaciated drainage basins in northwestern Canada (Kinaskan Lake (27.5 km²) in the Iskut R. watershed (1257 km²) of northwestern British Columbia; Kusawa Lake (142 km²) in the Tikhini R. watershed (4292 km²) of southwestern Yukon) are used to document responses in the sedimentary record to similar deglacial and Holocene climatic perturbations. From the time of withdrawal of valley glaciers at 11.5 to 7.8 ka Cal BP, sedimentation processes and rates change abruptly from basal units of thick sand deposits derived from turbidity currents to dominantly suspension settling of lacustrine silts and clays. While biologic proxies and regional climate reconstructions indicate this period is a time of warming and lower precipitation (Hypsithermal), thin and frequent sand units continue to 7.8 ka Cal BP indicating an abundant sediment supply, frequent turbidity currents and continuing strong connectivity to upper basin sediment sources. Between 7.8 and 2.5 ka Cal BP, silt and clay accumulation rates remain low despite renewed Neoglacial activity. Exhaustion in the supply of glacial sediments and the opening of upper-basin lake storage sites both contribute to the overall low accumulation rates. Thick, but infrequent, sand beds throughout this interval indicate extreme events driven by floods during the cooler and wetter Neoglacial period. Sands units are most likely derived from slope failures in lake margin fan-deltas. During the last 2000 years the frequency of sand beds declines significantly indicating reduced sensitivity of the sedimentary record to late Holocene hydrologic changes.