The river reinforcement above the main road was built in the 1930s. It is easy to see the differences in construction methods between the pre-war period and 1993. Here, the reinforcement is taller, and the thresholds in the riverbed are missing. Today, the reinforcement is covered in moss and blends more naturally into the landscape.

As you follow the river upstream, you will find a plant with many yellow flowers. This plant is called common tansy (Tanacetum vulgare) and naturally thrives in floodplains along rivers. It grows up to a meter tall with sturdy stems and blooms in August and September. Tansy is easily recognizable by its yellow flower heads, which form a flat cluster on top. The flower heads lack ray florets, making them look like small yellow buttons. Like many other plants in the daisy family, tansy is rich in oils and bitter compounds, giving it a distinctive scent.

Vegetation Along the River

Tansy has a long medicinal history in Europe. It was traditionally used to treat intestinal worms and toothaches. In dried form, it was stored with winter clothes to repel lice, fleas, and moths.

Locally, the plant was used to mask unpleasant odors. A story from the village of Flo tells how its people, who belonged to the Fosnes church, sometimes had to wait weeks for safe ice conditions before they could cross the lake to attend church. If someone died during this period, tansy was placed in the coffin to reduce the smell of decomposition.

Tansy also has a local nickname: ølkonge ("beer king"). This name originated because it was once commonly used as a flavoring in poor-quality liquor and beer. The name reinfann likely comes from the German Reinfarn, meaning "field fern," referring to the plant’s finely divided leaves, which resemble fern fronds. When knowledge of its medicinal properties spread to Norway in the Middle Ages, the German name was adopted and Norwegianized, even though the plant has nothing to do with reindeer.

Further up the valley, you will encounter lush alder forests mixed with rowan and birch. Fosdalen provides fertile ground for ferns such as lady fern, Athyrium filix-femina, and male fern, Dryopteris filix-mas. Here, lowland plants grow in the valley, while mountain plants appear at higher elevations.

One exception is alpine rockcress (Arabis alpina), a typical mountain plant that grows along the river reinforcement, outside its normal habitat. It is usually found near streams and on moist gravelly soil in alpine snowbeds. However, it often spreads along streams down toward the lowlands. This plant has large, striking white flowers and coarsely serrated leaves that extend high up the stem. It blooms from June to August.