The Allondon (French pronunciation: [alɔ̃dɔ̃]) is a river in France (Auvergne-Rhône-Alpes region) and Switzerland (canton of Geneva).

[2] Its source is located at 649 m (2,129 ft) elevation in the commune of Échenevex in the Ain department in eastern France.

It flows into the Rhône at the village of Russin in the canton of Geneva in Switzerland.

[2] It is home to the only recently known population of the rare insect Lachesilla rossica.

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