Lake Biel doubles aquatic plant diversity as water quality improves

Lake Biel has twice as many aquatic plant species as it did in the 1980s, SRF reported, with 24 species recorded in the latest survey. The improvement is linked to better water quality and reduced nutrient pollution.

Martina Küng, a scientific officer at the Bern cantonal water and soil protection laboratory, said the lake was no longer as heavily over-fertilised as it had been in the past. Wastewater treatment plants and a ban on phosphates in detergents have made the water clearer, allowing more light to reach deeper areas.

Water plants can now grow at depths of up to 13 metres. One key sign of the lake’s ecological recovery is the spread of stonewort algae, which are sensitive to nutrient pollution and indicate good water quality.

Stoneworts disappeared completely from Lake Biel in 1976 but now cover 64 per cent of the surveyed area. Fish can hide and spawn among the plants, while snails and aquatic insects also use them as habitat. The plants additionally help stabilise the lakebed.

The development of reed beds has also been positive overall, according to the canton. Reed beds provide valuable habitats for birds, fish and amphibians.

However, the effects of the hot summer of 2026 will only become clear in the coming years. Warmer water contains less oxygen, which can put pressure on some aquatic organisms. Climate change and invasive species are also creating new challenges for the ecosystem.

The cantonal Office for Water and Waste monitors the lake through divers who inspect eight test areas and record plants along the slope from the shore to the end of the vegetation. Aerial images are used to identify plants down to about five metres. Nuttall’s waterweed now covers around 10 per cent of the surveyed lake area, while the invasive quagga mussel is also affecting the habitat.

The aquatic plants will not be surveyed again for another 10 years.