WWII Sea Mines Cleared From Nordlicht Site of Germany’s Largest Offshore Wind Farm

Vattenfall has removed three unexploded World War II sea mines from the seabed at the planned Nordlicht offshore wind cluster, clearing a major safety hurdle ahead of construction next year.

Vattenfall said teams surveying the Nordlicht site, roughly 50 miles north of Borkum in the German North Sea, located and safely disposed of three sea mines during pre‑construction geophysical work. The removal moves the project a step closer to the start of construction in 2026.

The mines were detected during the company’s large‑scale seabed surveys carried out over the past two years. Initial geophysical data revealed magnetic anomalies that, on closer inspection with remotely operated vehicles (ROVs) this spring, were confirmed as unexploded ordnance. 

Each mine was assessed to contain an explosive charge with an energy equivalent to between 200 and 300 kilograms of TNT, Vattenfall said.

Disposal required a complex permitting and coordination exercise. Vattenfall secured regulatory approval for controlled detonations in September, but the permit limited exposure to large underwater noise events in the German Bight. 

To comply, the company coordinated timing with other nearby marine construction activity, notably pile driving by RWE, and planned operations to avoid overlapping high‑noise events.

A total of seven vessels were mobilised for the clearance operation, including support craft for the detonations, traffic control and ROV operations. The demolition was conducted by means of carefully planned controlled explosions, with an ROV used to position charges and monitor the site. 

To mitigate the acoustic impact of the blasts on marine life, Vattenfall deployed a 90‑metre “bubble curtain” system. This system consists of a double ring of tubes laid on the seabed that emits a continuous curtain of air bubbles to dampen underwater sound propagation.

Vattenfall reported the detonations and subsequent clearance went to plan and that the site is now free of the identified mines. 

The work was a necessary precursor to the construction of Nordlicht 1 and Nordlicht 2, for which Vattenfall made a final investment decision in March 2025. Nordlicht 1 is planned to deliver about 980 MW of capacity, with a second phase adding approximately 630 MW. The parks are expected to enter operation in 2028.

Legacy wartime ordnance remains a recurring issue for offshore wind development across the North Sea, where unexploded munitions from the two world wars still lie on the seabed. 

Vattenfall said the discovery was not unusual and highlighted the importance of comprehensive geophysical and ROV surveys during the site characterisation phase to identify hazards that must be cleared before foundation work and cable laying can begin.

With the mines removed, Vattenfall said it will press ahead with detailed preparatory work and mobilisation of supply chain partners ahead of the planned 2026 construction start.

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