**There is a newer version for this data package:** https://doi.org/10.25678/000GD7 In 2021, the Swiss Federal Office for the Environment (FOEN) tasked Eawag to deploy temperature monitoring stations in several lakes in view of a Swiss-wide temperature monitoring network. The monitoring station in Lake Hallwil (Canton Aargau) was introduced in July 2022 and it was operated until the end of 2024 by FOEN (financing) and Eawag (operation and maintenance). It consists of a thermistor chain with higher vertical resolution close to the surface. At the end of 2024, the measurement station was transferred from FOEN to Canton Aargau. Since January 2025, the measurement station is operated jointly by Canton Aargau (financing), FOEN (financial contribution to data processing and server infrastructure) and Eawag (operation and maintenance).