Precipitation in the Arctic is projected to increase dramatically over the next century. However, uncertainties surrounding precipitation seasonality remain. Lacustrine water isotope proxies are a powerful tool for reconstructing precipitation seasonality, but due to field accessibility limitations, little is known about seasonal variations in modern lake water isotope systematics in the eastern North American Arctic. We use modern lake water isotopes (d18O, d2H) measured on samples collected across a latitudinal gradient from northern Labrador to Ellesmere Island in the eastern North American Arctic, to evaluate precipitation isotope seasonality and evaporative enrichment in lakes through the ice-free season. We divided water isotope samples from 159 lakes into five latitudinal regions and find that lake water isotope values generally fall along their local meteoric water line. The few lakes that are evaporatively enriched outside the range of meteoric water are small and non-throughflowing. Although we observe some variability within each region, we generally find a latitudinal gradient in the isotopic composition of lakes along the transect: southern lakes tend to reflect amount-weighted mean annual precipitation isotopes, whereas northern lakes tend to reflect amount-weighted summer precipitation isotopes. We investigated this intra-regional variability by evaluating four lakes near Iqaluit, Nunavut that were sampled approximately biweekly through the ice-free seasons of 1994-1996 CE (Sauer, 1997). These lakes reflect mean annual precipitation and become slightly evaporatively enriched throughout the ice-free season, but remain within the range of meteoric water isotopic variability. We created a box model for these four lakes and found that the isotopic composition of lake water is most sensitive to changes in the annual runoff to precipitation ratio (R/P). Therefore, we infer that the latitudinal gradient we observe in lake water isotope seasonality is driven by a northward proportional increase in the amount of precipitation that falls during the ice-free season as well as a poleward increase in R/P, resulting from reduced vegetation cover. Accordingly, most lakes in the eastern North American Arctic are good targets to study variations in precipitation isotopes over time because they are not strongly impacted by evaporative enrichment. However, we reaffirm that a strong understanding of lake water isotope and proxy systematics for a target lake is critical to know which season will be reconstructed by a given proxy.