52’ / HD + 4K
Between the Black Forest and the Vosges it’s not only the Rhine that flows slowly northwards but also another waterway, hidden from view. The largest groundwater reservoir in Europe forms an underground river in the Upper Rhine Valley, which gives rise to wetlands of unique beauty – home to rare animals and plants. Underwater cameraman Serge Dumont, whose work has won numerous awards, has captured this unknown world in breathtaking sequences. He gets closer to the inhabitants of this biotope than any other documentary maker before him. Pike and great crested grebe pursue their prey right in front of his lens. This wildlife filmmaker, who is a professor of biology at Strasbourg University, has managed to record behaviour patterns of fish and birds never seen before. The film also reveals the fascinating world of insects, amphibians and microorganisms in these biotopes. For the first time, Serge Dumont was able to film dragonflies laying their eggs in plant stems up to two metres below the surface of the water. It’s their way of ensuring that the eggs don’t dry out when the water level drops. The film transports us into an alien world filled with bizarre creatures we would never suspect lived right on our doorstep. The wetlands in the Upper Rhine Valley owe their existence to the constant flow of clean, unpolluted groundwater. This is increasingly affected, though, by the excessive use of fertilisers and pesticides in agriculture, which poses a real threat to the small paradise habitats. 'The Invisible River' shows uniquely the great biodiversity dependent on pure groundwater – and just how important it is to protect it.
Producer: Längengrad Filmproduktion, Seppia
Production year: 2019
Broadcasters: SWR, WDR, arte, France Télévisions
Languages: English, German, French