The survey vessel Proteus of Liverpool is carrying out geophysical survey operations in and around the Gwynt y Môr offshore wind farm.
The vessel started the survey operations on 21 April, a Notice to Mariners said.
Gwynt y Môr is the world’s second largest operating offshore wind farm, located off the North Wales coast.
Fully commissioned in June 2015, the 576MW project comprises 160 Siemens 3.6MW turbines.
The wind farm is a GBP 2 billion partnership between innogy, Stadtwerke München GmbH, and Siemens.