Since 2012, the depths of Lake Geneva have not been properly replenished with oxygen because of a lack of cold weather.
Normally, cold winter weather cools surface water. This denser cold water then falls creating a mixing action, which oxygenates the water. The colder the surface the more vigorous the mixing. According to the Commission internationale pour la protection des eaux du Léman (CIPEL), this mixing only reached depths of 135 metres this winter, less than half the lake’s maximum depth of 309 metres.
Low levels of oxygen increase the amount of phosphorous released from the lake bed. This increase algae growth, which in turn further reduces oxygen levels. This vicious cycle is increased further by phosphorous added to the lake by human activity.
Human activity is quietly affecting the lake in more ways than one.