Gottorf Castle moat 

Problem: Sludge formation, algae growth, fish death

Project highlights

Unique pilot project for MELUND and the city of Schleswig 
Creation of open water by desludging without dredging
Innovative, natural and gentle process

The starting point

Think smart to save money: ecological water restoration

Anyone who looks after natural bodies of water will well know: By the time you notice symptoms of poor water quality – whether fish death, unpleasant odours or algae growth – the underlying problem is often well advanced. This was the case in the Burgsee lake and moat of Gottorf Castle near Schleswig. The increasing incidence of fish deaths led the town and the state of Schleswig-Holstein to commission an expert opinion to determine the causes. The result was alarming: The entire biological cycle of the nutrient-rich water had already been severely disrupted.

A multi-faceted problem

The high phosphorus content in the tributaries of the bodies of water surrounding the island serves as a nutrient supply, especially for algae, and leads to an intense algae bloom, especially in the summer months. This huge increase in biomass produces sludge with a high organic content, which at the same time significantly reduces the oxygen content and volume of the water: Precise measurements revealed the presence of massive sediment deposits of up to 1 m in height, which meant that the water depth at low levels was just 50 cm. Instead of this water being a suitable habitat for fish, it is actually an unstable ecological system with only a low self-healing capacity.

Removing the sludge by conventional dredging would be a very expensive solution, because about 10,000 m³ sediment would have to be taken from the two sections of the castle moat, which were especially affected. Due to the increased phosphate input, this sediment would also have to be safely disposed of in landfill. The total estimated cost was around 1 million euro. This was too high, so the project heads turned to OASE PROFESSIONAL in search of a more innovative solution.


The solution

A holistic approach for balancing the unstable system with SchlixX Plus 

In order to restore biological balance, it is necessary to use one solution to address all problem areas: Effective and gentle reduction of the sludge increases the open water volume and thus the amount of available space for fish. At the same time, the sludge reduction minimises the oxygen consumption by the sediment and additionally supplies the water with more oxygen. SchlixX Plus, which has just received the German Award for Sustainability Projects, has been created for precisely this purpose. 

An innovative pilot project


The city of Schleswig and the MELUND Schleswig-Holstein were impressed by OASE's holistic approach and decided to commission a pilot project: Over the course of six months, SchlixX Plus would be trialled on two test surfaces in the moat. Hamburg-based company KLS was responsible for testing the water and sediment, as well as for all monitoring and the preparation of reports. During the pilot phase, the water was to be kept at a minimum temperature of 8°C, so 28 April 2021 was the perfect date for the application. Sileswig's Mayor Stephan Dose and State Secretary Dr. Dorit Kuhnt joined the other officials to witness the occasion.

Project fact sheet

Project nameGottorf Castle moat
Type of waterFresh water with interference from salt water from the shallows
Type and sizeMoat: 3 hectares, Burgsee: 18 hectares
ProblemSludge formation, algal bloom, fish death
Product appliedSchlixX Plus
Period and type of applicationApril 2021: 350 kg of SchlixX Plus applied to two test surfaces
Result of the applicationEvaluation of the pilot project October 2021
Expected resultAfter three applications: 30 to 60 cm sludge removed

You would also like to implement a project like this?

Contact our consultants