| Mandalselva | |
| Name Other: | Mandalsåni / Marna |
| Subdivision Type1: | Country |
| Subdivision Name1: | Norway |
| Subdivision Type3: | County |
| Subdivision Name3: | Agder |
| Subdivision Type4: | District |
| Subdivision Name4: | Sørlandet |
| Subdivision Type5: | Municipality |
| Subdivision Name5: | Åseral, Lyngdal, Lindesnes |
| Length: | 115km (71miles) |
| Discharge1 Location: | Kjølemo, Mandal |
| Discharge1 Avg: | 85m3/s |
| Discharge1 Max: | 970m3/s |
| Source1: | Øre lake |
| Source1 Location: | Åseral, Agder, Norway |
| Source1 Coordinates: | 58.5783°N 7.3967°W |
| Source1 Elevation: | 260m (850feet) |
| Mouth: | Mannefjorden |
| Mouth Location: | Mandal, Agder, Norway |
| Mouth Coordinates: | 58.02°N 7.4572°W |
| Mouth Elevation: | 0m (00feet) |
| Basin Size: | 1800km2 |
Mandalselva, Mandalsåni, or Marna (English: Mandal River, Norse, Old: Mǫrn) is a river in Agder county in Norway. The river has its origins in the mountains between Ose in Setesdal and the Upper Sirdal valley. The river flows south to its mouth at the North Sea at the town of Mandal. The river is 115km (71miles) long and flows through the municipalities Åseral, Lyngdal, and Lindesnes. The largest tributaries are Monn, Logna, Skjerka, Kosåna, Logåna, and Røyselandsbekken. Skjerka, Monn and Logna all flow into the lake Øre in Åseral which is considered the beginning of the main Mandalselva river. The river passes through the villages of Kylland, Bjelland, Laudal, Heddeland, Øyslebø, and Krossen.[1]
Hydropower development of the river on a larger scale started in 1930. At present there are six power plants along the river and its upper tributaries: Logna, Smeland, Skjerka, Håverstad, Bjelland, and Laudal.
The drainage basin covers an area of 1800km2. The mean flow of water in the river is 85m3/s. During flooding periods in the spring and autumn, water flow can be far greater. The highest stream flow in recent times were measured in October 1987, when it passed about 970m3/s at Kjølemoen in Holum.[2]
The original salmon stocks are extinct as a result of acid rain, but extensive liming has led to a better environment in the river, and a new salmon stocks are established. It was caught of salmon and sea trout in Mandalselva in 2015.[3] [4]