In recent years, many water reservoirs have been facing the negative consequences of eutrophication, caused by an excessive influx of nutrients, especially phosphorus and nitrogen. These nutrients support the overgrowth of cyanobacteria and algae, which significantly deteriorate water quality. A prime example of such a situation is the Mšeno water reservoir in Jablonec nad Nisou, which has long struggled with recurring cyanobacterial blooms and elevated phosphorus levels. The Mšeno reservoir is an important water management structure in the Liberec Region, primarily serving a flood protection function but it also offers visitors a popular site for active recreation.
The natural regulation of nutrient levels and the balance of aquatic ecosystems is often ensured by shoreline reed zones. However, these are disappearing from many locations due to factors such as steep reservoir banks, grazing by waterfowl, or destruction caused by human activity. Restoring these natural zones is technically challenging and financially demanding. As an alternative, so-called floating vegetated islands can be implemented.
Floating vegetated islands are artificially created platforms planted with reeds and other suitable plants. These islands consist of synthetic support mats equipped with integrated buoyancy systems. Plants root directly into these structures, forming a dense network of roots that hang freely into the water. In such conditions, the root systems develop far more intensively than in traditional substrates and effectively absorb nutrients from the water. At the same time, they provide a habitat for microorganisms that break down organic matter, thus contributing to natural water purification.
One of the main benefits of these islands is the shading of the water surface, which reduces sunlight penetration and limits cyanobacterial growth. The plants also enrich the water with oxygen, improving conditions for aerobic decomposition. The ecological function is equally important – vegetated islands offer refuge for fish, amphibians, birds, and insects, thus supporting aquatic biodiversity and naturally enriching the water ecosystem.
In October 2021, the city of Jablonec nad Nisou installed floating vegetated islands on the surface of the reservoir as part of a broader strategy to combat cyanobacterial blooms. A total of 38 islands were installed on the Mšeno II reservoir, each measuring 1.18 m × 2.50 m, resulting in a combined area of 112 m². The islands are modular and interconnected to form a larger island complex covering more than 700 m². To prevent the reintroduction of accumulated biomass into the nutrient cycle, the islands are moved once a year.
Combined with other measures implemented at the Jablonec reservoir, this type of protection has proven promising. Monitoring has shown a decrease in phosphorus concentrations and improved water transparency.
Floating vegetated islands thus represent an innovative and economically viable tool that can be used in both urban and rural environments. Their successful implementation in Jablonec and Nisou may serve as an inspiration for other municipalities and water managers seeking effective and environmentally friendly solutions to problems such as cyanobacterial overgrowth, nutrient pollution, and the loss of natural balance in aquatic ecosystems.

Čistá voda, zdravé životní prostředí | Photon Water
Proti sinicím ochrání přehradu opět ultrazvuk a plovoucí zelené ostrovy - Jablonec nad Nisou
Ultrazvuk a plovoucí ostrovy se osvědčily, ochrání jabloneckou přehradu i letos - Jablonecký deník
 

DIRECT SDGs:
SDG 6 - Sustainable water management

INDIRECT SDGs:
SDG 15 - Promote sustainable ecosystems and widen biodiversity
 

SDG 6 - With a good water management is possible to keep s good water  quality
SDG 15 - Return back to natural biodiversity and widen ecosystem
 

What elements contribute to the overgrowth of cyanobacteria and algae in water?
What functions do vegetated islands serve?
What are the reasons for the disappearance of natural shoreline reed zones?
 

The installation of vegetated floating islands helps reduce nutrient concentrations and limit the growth of cyanobacteria, while also supporting the restoration of natural habitats in urbanized landscapes. By creating a spatially diverse biotope with rich vegetation and intricate root structures, new opportunities arise for the presence of insects, fish, and birds, significantly enhancing biodiversity. Floating islands thus represent a practical solution that combines water management functions with nature conservation, benefiting not only the ecosystem but also local residents who use the reservoir for recreation.

Marcela Beková
Spolek absolventů a přátel zemědělské školy v Chrudimi z.s.