The Hermance () is a river in France and Switzerland, that discharges into Lake Geneva. It rises near Loisin in Haute-Savoie, France, at elevation. In its lower half, downstream from Veigy, it marks the Swiss-French border. It flows into Lake Geneva between the villages Hermance (Switzerland) and Chens-sur-Léman (France), at elevation. Its total length is ( according to the Sandre database), of which 6.5 kilometres on the border. Its catchment area is , of which 37 km2 in France.
Flood control and other river maintenance issues are regulated under the 1959 Hermance River Agreement.Ariel Dinar et al., Transboundary Water Conflict, Negotiation and Cooperation, World Scientific, 2007. , . p. 185
See also List of rivers in France List of rivers in Switzerland
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