Demonstration sites
Select a site to see it on the map.
Site description
The Dröda Reservoir is a eutrophic water body in Saxony, Germany, with a surface area of 1.1 km², a maximum depth of 36 m, and a mean depth of 13 m. Built in 1971, it supplies drinking water to four cities and 35 municipalities in the Vogtland region, while also providing flood control, low-flow support, and hydropower. Its 53 km² catchment is dominated by agriculture, and diffuse nutrient inputs have increased algal biomass in recent decades. With a short water residence time of about one year, the reservoir is especially vulnerable to external nutrient loading, making catchment-based interventions essential.
Restoration goals
The aim is to reduce diffuse phosphorus inputs at the reservoir’s main inflow and recover phosphorus for reuse in agriculture. By binding phosphorus with iron-based coagulants and recycling the captured flocs, the project supports both water quality improvement and a circular phosphorus economy.
Currently used restoration measures
A catchment-based approach is applied at the reservoir’s main inflow, where an iron-based coagulant is dosed into the water to bind phosphorus and particulates. The resulting dense flocs settle in the reservoir and are later harvested for reuse as an alternative phosphorus fertiliser. This measure directly reduces algal blooms, improves water quality, and supports circular nutrient reuse. It is cost-effective, sustainable, and transferable to other reservoirs and natural lakes with significant external nutrient inputs and surface inflows. By combining phosphorus removal with recovery, the approach demonstrates how restoration can be aligned with resource recycling and climate resilience.
Site description
The Vrchlice Reservoir is a eutrophic water body in Central Bohemia, Czech Republic, with a surface area of 0.94 km², a maximum depth of 32 m, and an average depth of 9 m. Its 97 km² catchment is dominated by agriculture, and the reservoir retains water for about half a year. Constructed in 1974, it supplies drinking water to around 80,000 people in the Kutná Hora and Čáslav regions, and also serves for flow maintenance, flood protection, hydropower, and local irrigation. In recent decades, internal phosphorus release has contributed to high phytoplankton biomass, raising concerns about water quality.
Restoration goals
The goal is to reduce internal phosphorus loading and secure drinking water quality while promoting resource recovery. A solar-powered pump transfers phosphorus-rich hypolimnetic water to the surface, where it is filtered to remove phosphorus. The cleaned water is returned to the hypolimnion, and the captured phosphorus is prepared for potential reuse.
Currently used restoration measures
A solar-powered pump transfers phosphorus-rich hypolimnetic water from the deepest part of the reservoir to the surface. There, it passes through a filtration system that removes phosphorus before the treated, phosphorus-poor water is returned to the hypolimnion below the thermocline. This reduces internal phosphorus loading and suppresses algal growth. The filter material is periodically replaced and exploited for phosphorus recovery, with the potential for reuse in agriculture, linking water quality improvement with circular nutrient management. In the catchment, upstream pre-dams and ponds such as Hamerský, Roztěž, and Lázně trap sediments and nutrients from inflows, while wastewater treatment plants have improved phosphorus removal efficiency. Together, these measures improve reservoir water quality and safeguard drinking water supply.
Site description
Lake Mustijärv is a small, shallow lake (≈1 ha, mean depth 2 m, max depth 3.8 m) in central Estonia. In 2016, it was restored through complete desiltation, creating deep sediment basins to concentrate nutrient-rich inflows. The dredged sediment was successfully tested as fertiliser in field and mesocosm studies, making it a pioneering case of lake restoration combined with nutrient recycling. However, high external nutrient inputs quickly refilled the sediment pool, and by 2018 the lake had again reached hypertrophic conditions. Today, both external catchment loading and internal phosphorus release continue to drive poor water quality.
Restoration goals
The goal is to improve water quality by reducing both internal and external phosphorus loading. Restoration also aims to demonstrate sustainable sediment removal and recycling as fertiliser, highlighting cost-efficient, environmentally sound, and circular approaches to lake restoration.
Currently used restoration measures
Restoration focuses on selective sediment removal from hot-spot accumulation areas, making the intervention more cost-efficient and environmentally friendly than complete dredging. Sediments accumulated since 2016 are tested again for fertiliser value. Additional measures include installing sedimentation ponds at inflows to trap nutrient-rich particles before they enter the lake. This reduces external loading and supports long-term improvement of water quality. The approach integrates catchment and in-lake measures, enabling both phosphorus retention and recovery, and provides a scalable demonstration of circular, resource-efficient restoration.
Site description
Lake Fure is the deepest lake in Denmark, located north of Copenhagen on the island of Zealand. With a maximum depth of 38 m, mean depth of 13.5 m, and an area of 9.4 km², it is a large stratifying lake with a 79 km² catchment dominated by urban land use. Since the 1970s, it has suffered from eutrophication, largely due to phosphorus inputs, which promoted excessive algal blooms. From 2003 onwards, artificial oxygenation was applied to reduce sediment phosphorus release, but this measure had limitations and could not secure long-term recovery. Therefore, new strategies for internal phosphorus removal and recycling are now being tested within the FERRO project.
Restoration goals
The goal is to reduce internal phosphorus loading by removing phosphorus released from the sediment and recycling it as fertiliser. Innovative pump-and-filter technologies will capture phosphorus-enriched hypolimnetic water, supporting sustainable restoration while closing nutrient loops between lake and agriculture.
Currently used restoration measures
Until recently, artificial oxygenation was used in deep lake areas to prevent phosphorus release under anoxic conditions. Within FERRO, this approach has been stopped, allowing phosphorus to be released naturally from sediments bound to reduced iron compounds. Solar-driven pumps are now being installed to bring phosphorus-rich hypolimnetic water to the surface. The water passes through an iron-based filter system, where phosphorus is trapped and recovered as a product suitable for agricultural fertilizer use. This approach directly reduces internal phosphorus loading while also demonstrating how restoration can support a circular phosphorus economy.
Site description
Lake Ormstrup is a shallow Danish lake (11 ha) with an average depth of 3.2 m and a maximum depth of 5.5 m. Decades of nutrient loading from agriculture and intensive duck rearing have caused extreme eutrophication, with phosphorus concentrations reaching 500–1000 µg/L. The lake has experienced algal blooms, low water clarity, and loss of biodiversity. In recent years, it has been the focus of Danish lake restoration research, including biomanipulation and large-scale sediment dredging in 2024. Within FERRO, the lake provides a unique opportunity to test sediment recycling approaches under controlled conditions in a catchment that is representative of intensive agricultural pressures.
Restoration goals
The main goal is to document the fertiliser value of dredged lake sediments and test whether adding biostimulants enhances nutrient recovery. By linking lake restoration with agricultural reuse, the project aims to demonstrate the benefits of circular nutrient management in shallow, eutrophic lakes.
Currently used restoration measures
Lake Ormstrup has undergone major restoration interventions, including biomanipulation to reduce fish predation on zooplankton and large-scale sediment dredging in 2024 to remove nutrient-rich deposits. Within FERRO, dredged sediments are tested in the agricultural catchment to evaluate their potential as fertiliser, both with and without added biostimulants. This experimental setup provides evidence for the reuse of lake sediments as a resource while reducing phosphorus levels in the lake. The approach links lake restoration directly with agricultural nutrient recycling, aiming for cost-efficient, environmentally friendly, and scalable solutions to tackle eutrophication in shallow lakes.