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​Restauration of lakes and fjords with pure oxygen

​Liquid oxygen cryotank

​Control panel

Service vessel with diffusor​

Fish enjoying the oxygen​

​Oxygen depletion caused by eutrophication is a common problem in many lakes and fjords. It is caused by run-off of nutrients from farmed land and by household and industry sewage. Major efforts are well underway to address these causes but it will unfortunately take a considerable amount of time for the full impact to be seen. The internal load will continue for decades.

​Restoring lakes and fjords with pure oxygen (O2) has an immediate effect. Oxygen prevents the release of phosphorus and toxic gases (hydrogen sulphide and ammonia) from the sediment, accelerates the decomposition of “past sins” and breathes new life into the environment.

As the only company in the EU we develop, install and service oxygenation systems for deep lakes and fjords. We have more than 20 years of experience with injecting pure oxygen into deep bodies of water.

The method is gentle towards the environment. Oxygen is a 100% natural substance with no adverse side effects.

Our unique diffuser systems are highly effective. Up to 95% of the injected oxygen dissolves and is distributed to all parts of the hypolimnion without disturbing the thermocline. The oxygen saturation in the hypolimnion can precisely be managed using a land-based control panel.

An oxygenation system consumes very little energy. It runs with the evaporation of liquid oxygen. Each system is individually developed, designed and adjusted for the particular conditions in a given lake or fjord.

We are happy to provide rough estimates of oxygen demand and of the cost of installing and servicing.​

​Service work


​Marking buoy

Lake Fure and Lake Hald

Lake Fure and Lake Hald were for many years suffering severe problems with poisonous H2S and cyanobacterial bloom which caused death of fish and prohibition of bathing. In both lakes these problems rapidly vanished after only 1-2 years with oxygenation.

​Since 2003 Multidyk has been restoring Lake Fure with pure oxygen. Lake Fure is located close to Copenhagen and has an area of 10 km2 and a depth of 38 metres - the deepest lake in Denmark. After only a few years the results are significant and well documented: Lake Fure is changing remarkably for the better after decades in very poor environmental conditions.​

In Lake Hald, 31 metres - the second deepest lake in Denmark - the first attempt of injecting pure oxygen into deep water was made in 1985. Over time the technology has been developed and the efficiency has improved radically. In 2006 we installed our newest generation of oxygenation systems in Lake Hald. Today Lake Hald is one of the cleanest lakes in Denmark!

In the figures are shown “before” and “now” situations for the average summer concentrations of phosphorous together with the average secchi depth.

In the figures are shown “before” and “now” situations for the average summer concentrations of phosphorous together with the average secchi depth.

The effect of the oxygenation is an impressive reduction of the internal loading of phosphorous which leads to a reduction of the production of plankton algae causing a much larger transparency in the lake water.

In Lake Fure the underwater vegetation now grows down to 8.5 metres and in Lake Hald to 6.5 metres. And animal life is widely spread even in the deepest parts of the lakes.

The restorations of Lake Fure and Lake Hald are considered by many experts to be the most successful environmental projects in Denmark. Hypolimnic oxygenation has dramatically changed the environmental conditions in two lakes of great biological and recreational value.

Restoration of Lake Fure, EU-LIFE-project: EU-LIFE-project:  Final Report, page 44-45: 


 "The oxygenation project has demonstrated that it is possible to achieve a significant and, above all, rapid improvement in the environmental condition in deep lakes with lack of oxygen in the hypolimnion.

In many similar lakes in the EU there are the same problems as in Lake Fure. For decades phosphoric waste-water has been discharged to the lakes resulting in accumulation of a pool of phosphorus in the sediments. The consequent seasonal internal load will prevail for many decades and will be one of the reasons why the 

Directive objectives cannot be met within the time frames even if the nutrient supply is reduced significantly.

In a transitional period, brief or long, the oxygen supply can contribute to substantial improvements in the conditions of lakes and the survival of threatened species."


Røverdal 19, Dollerup

8800 Viborg

​​Telefon: 86 63 85 46

Mobil: 20 41 10 03

Mail: multidyk@fiberboks.dk

CVR: 91643952​