Oxygen isotope distributions from lacustrine carbonates provide insights into climate and hydrological change, but it is difficult to isolate the influences of catchment precipitation delta 18O, water temperature, and evaporation on lacustrine carbonate delta 18O values. Recent work shows the potential for using a combination of clumped (Delta 47) and triple oxygen isotope (Delta iota 17O) measurements to identify the roles of temperature and evaporation on carbonate delta 18O values in lakes, allowing precipitation delta 18O values to be inferred and facilitating paleoclimate reconstructions. However, modern calibration of this approach has been mostly limited to arid regions with a high ratio of evaporative losses over inputs (XE) and low relative humidity (h < 0.7). Developing this tool for paleoclimate and paleoelevation reconstructions requires expanding the modern calibrations to a greater range of climatic and hydrologic conditions. We sampled four lakes in different hydrologic states under a single, high humidity climate regime (h = 0.7-0.9) in the Lake Junin region of central Peru. Clumped isotope temperatures from lake carbonates reflect water temperatures during carbonate formation. Lake hydrology is the main control on the Delta iota 17O values of carbonates and waters: Delta iota 17O values are lowest in the larger lakes with higher XE when compared to smaller, headwater lakes where evaporation is minimal and Delta iota 17O is indistinguishable from that of precipitation. Reconstructed unevaporated catchment precipitation delta iota 18O (delta iota 18Orucp) values from lake waters rely on accurate characterization of Alake , the triple oxygen isotope evaporation slope. We explore the influence of humidity on Alake using both new observations and modeled data. Accounting for local humidity improves Alake estimates, which allows for more accurate reconstructions of delta iota 18Orucp. We generate a delta iota 18Orucp value of-15.2 +/- 2.1%o from modern carbonates and waters (n = 15) in the Lake Junin region, which is similar to amount weighted mean annual precipitation-14.1 (+/- 2.2%o). This study illustrates that (1) Delta iota 17O can be used to differentiate between lakes with differing XE in humid climates, (2) lake carbonate Delta iota 17O and delta 18O values can be used to evaluate the influence of evaporation on lake water delta 18O values in a range of climates, and (3) modeling Alake under appropriate humidity conditions improves delta iota 18Orucp estimates from lake carbonate Delta iota 17O.(c) 2022 Elsevier B.V. All rights reserved.