The dataset compiles water isotope measurements of 66 lakes, sampled in Central and Eastern Yakutia during a summer field campaign in August and September 2021 (RU-Land_2021_Yakutia). Additionally, there are isotope data of a single rain event, received during the campaign.The investigated lakes are located in four different study areas in the Sakha Republic, Russia: in the mountainous region of the Verkhoyansk Range within the Oymyakonsky and Tomponsky District (EN21401 - EN21415), and in three lowland regions of Central Yakutia within the Churapchinsky, Tattinsky and the Megino-Kangalassky District (Event EN21416 - EN21467). One lake (EN21160) is centrally located in the city of Yakutsk, the capital of the Sakha Republic. Baisheva et al. (2022) gives an overview of the lakes studied and the corresponding hydrochemistry.Surface water samples (0 – 0.5 m) for measurement of stable water isotopes (δ18O, δD) have been taken for all lakes. If the lakes were deeper than five meters (≥ 5 m), water samples of the middle and bottom water (MW, BW) of the lake were taken, too. Where it was available and reachable, there are also water isotope data from in- or outflow (IF, OF).For two greater lakes, there are one or even more depth profiles composed of several isotope samples from different depths (EN21112, EN21116, EN21124¸ EN21160; numbers at the end indicate different sampling depths).There were two different methods of sampling: Either water for isotope measurements was directly sampled from the lake into 30 ml narrow-mouth PE bottles, filled to the top and closed tightly. Otherwise water samples were taken with an UWITEC water sampler (2 L), filled into a larger sample container (2 L Whirl-Pak®) and subsampled in 30 ml narrow-mouth PE bottles as soon as possible afterwards.The single rain event was sampled on the 22nd of August 2021 at one of the field camp sites, close to the lake EN21427. A dry, clean plastic container was placed outside for receiving the rain. The subsampling was done immediately after the event by rinsing it into 30 ml narrow-mouth PE bottles, filled to the top and closed tightly. All samples were stored cool and dark as soon as possible until analysis.All data were collected and processed by scientists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), Germany, the University of Potsdam, Germany, and the North-Eastern Federal University of Yakutsk (NEFU), Russia.Oxygen and hydrogen isotope analyses were carried out at the ISOLAB Facility at Alfred Wegener Institute in Potsdam (hdl:10013/sensor.ddc92f54-4c63-492d-81c7-696260694001) with mass spectrometers (DELTA-S Finnigan MAT, USA): hdl:10013/sensor.af148dea-fe65-4c87-9744-50dc4c81f7c9 and hdl:10013/sensor.62e86761-9fae-4f12-9c10-9b245028ea4c employing the equilibration method (details in Meyer et al., 2000). δ18O and δD values are given in per mill (‰) vs. Vienna Standard Mean Ocean Water (VSMOW) as the standard.N indicates the number of measurements per sample. If N > 1, the mean isotope value of the sample was calculated from the individual measurement results. The standard deviation includes all measurements of the individual sample, which is generally better than the external (or machine) error. The external errors of long-term standard measurements for hydrogen and oxygen are better than 0.8‰ and 0.10‰, respectively (Meyer et al., 2000). The second order parameter d excess was computed according to: d excess = δD – 8 * δ18O (Dansgaard, 1964). For the calculation of d excess, the respective mean values were used.