Otra River in Southern Norway

The Otra River in southern Norway is currently experiencing variable flows, highly influenced by regulation from hydropower operations, but not as severely impacted by drought as major European rivers in 2025. As of the most recent updates, real-time flow figures at specific gauges (e.g., Bykil) show values as low as 0.86 m³/s at some tributary points, though discharge at the river mouth is legally maintained at a minimum of 50 m³/s to meet environmental and hydropower requirements.fis.freshwatertools+2​

Key Trends and Hydrology

• Runoff in the Otra basin is generally stable, with future projections indicating a pattern of increased winter flows and reduced summer flows, driven by climate change impacts.fis.freshwatertools​

• Hydropower remains a major driver of water level and flow fluctuation, causing rapid changes in some stretches, but salmon spawning and ecological monitoring have improved due to stricter flow regulation in recent years.smartwatermagazine​

• About 40% of the Otra basin has been hydrologically altered for electricity production, and several stretches are classified as ‘heavily modified’ due to these changes.fis.freshwatertools​

Ecological and Management Notes

• Water quality concerns have persisted due to acid precipitation and hydropower impacts, but ongoing management has led to moderate improvements in salmon habitat and overall river health.smartwatermagazine+1​

• Real-time monitoring by local associations ensures hydropower operators maintain required minimum flows, supporting both fish populations and downstream communities.smartwatermagazine+1​

The Otra currently maintains stable regulated flows, with basin management balancing hydropower, ecological health, and local water supply needs.earlyfloodalert+2​

1. https://kartverket.no/en/at-sea/se-havniva/result?cityid=28&city=Otra&widget=true&language=nb&id=28
2. http://fis.freshwatertools.eu/index.php/otra.html
3. https://smartwatermagazine.com/news/norwegian-university-science-and-technology-ntnu/norwegian-rivers-need-be-better-protected
4. https://www.nature.com/articles/s41598-024-53637-5
5. https://earlyfloodalert.com/en/river.php?river=Otra
6. https://flyfishcircle.com/country/norway/location-group/otra-river
7. https://www.riverapp.net/en
8. https://www.visitnorway.com/things-to-do/outdoor-activities/fishing/salmon/