Observed discharge at national stations: https://www.hydrodaten.admin.ch/en/seen-und-fluesse/messstationen-zustand (no online download, for ordering contact the " Data service Hydrology" see here)
New (June 2025): Tool to evaluate degree of anthropogenic influence at Swiss national gauging stations: https://www.bafu.admin.ch/bafu/de/home/themen/wasser/fluesse-und-baeche/wasserfuehrung-und-abflussregime-der-fliessgewaesser/beeinflussung-des-abflusses.html
CAMELS-CH: https://zenodo.org/records/10354485, paper: https://essd.copernicus.org/articles/15/5755/2023/essd-15-5755-2023.pdf, GitHub: https://github.com/camels-ch/camels
Hourly discharge data base by M. Kauzlaric: https://zenodo.org/records/7691294
Simulated monthly runoff values and river regime classification for entire Switzerland are available from simulations completed by the WSL for the FOEN/BAFU (link updated Feb 2024); (new) this includes simulations for future periods. The data set keeps on migrating, ask google for called "mean monthly and annual runoffs + BAFU".
Climate change data sets, Hydro-CH2018 https://www.nccs.admin.ch/nccs/de/home/klimawandel-und-auswirkungen/schweizer-hydroszenarien/hydro-ch2018-datensaetze.html
Corresponding hydrological simulations available on https://hydromapscc.ch
Discharge simulations corresponding to 2011 scenarios available from the CCHydro project. Time series at all stations listed under "Gauges" are available, WSL. Underlying model: Prevah (paper)
Stream network https://opendata.swiss/en/dataset/swisstlm3d-gewassernetz
Hydro background map: https://opendata.swiss/en/dataset/generalisierte-hintergrundkarte-zur-darstellung-hydrologischer-daten
Location of measurement stations: https://opendata.swiss/en/dataset/basismessnetz-oberflachengewasser
Shapefiles of the catchments corresponding to above: https://www.bafu.admin.ch/bafu/de/home/themen/wasser/zustand/karten/geodaten/einzugsgebiete-der-hydrometrischen-messstationen-der-schweiz.html
The Swiss Federal Office for the Environment published a database that gives advanced metadata on their gauging stations at this link, the file is currently in German only: "Messnetzkonzept Hydrologie - Zuordnung aktuelle Stationen zu Anwendungsgebieten Stand 2022.xlsx"
Cantonal resources (incomplete list, updated on 02 June 2021 based on a list by M. Floriancic in this Supplement from this paper).
Canton de Vaud: http://www.vhv.ch/ (completely renewed, online download)
Canton de Neuchâtel: http://www.vhne.ch/
Canton de Genève: http://www.vhg.ch/
Kanton Aargau: https://www.ag.ch/app/hydrometrie/station/
Kanton Basel Landschaft: https://hydro-jb.bl.ch/main_hydro.htm
Kanton Bern: https://www.bve.be.ch/bve/de/index/wasser/wasser/messdaten/fliessgewaesser.html
Kanton Graubünden: https://www.seba-hydrocenter.de/projects/index.php?user=anuchurpub
Kanton Luzern: https://uwe.lu.ch/themen/gewaesser/hydrometrie/abfluss_und_seepegel
Kanton Schaffhausen: http://www.hydrodaten.tg.ch/app/index.html#Abfluss
Kanton Solothurn: https://so.ch/verwaltung/bau-und-justizdepartement/amt-fuer-umwelt/umweltdaten/wasser/hydrometrie/daten/#
Kanton St.Gallen: http://www.hydrodaten.sg.ch/#Abfluss
Kanton Thurgau: http://www.hydrodaten.tg.ch/app/index.html#Abfluss
Kanton Ticino: https://www4.ti.ch/dt/dc/uca/temi/corsi-dacqua/corsi-dacqua/compiti/idrologia-e-pericoli-naturali/idrologia/
Kanton Zürich: https://awel.zh.ch/internet/baudirektion/awel/de/wasser/messdaten/abfluss_wasserstand/jb_abfluss.html