We licence activities:

• in the Welsh sea - such as a marker buoy or a pontoon 
• over the Welsh sea - including something above or over-hanging the sea such as a bridge or cantilever
• under the Welsh sea - including the ground under the sea and and anything resting on it such as a wreck
  
  

The Welsh sea

The 'Welsh sea' reaches from areas submerged at mean high water springs and extends to the Welsh economic zone.  

The licensable area also includes waters which are closed against the regular action of the tide by, for example, a lock, but into which seawater can flow. 

Mean high water springs

In general, 'mean high water springs' is the average high tide mark.

It is reached if the ground is made wet from the normal ebb and flow of the tide or if there is evidence, such as marking or growth, that suggests the tide has reached a point in the past.

Mean high water may include rivers and estuaries since these are also affected by the ebb and flow of the tide.

The height of mean high water springs is the annual average of two successive high waters during a 24-hour period in each month when the range of the tide is at its greatest (spring tides).

How to find mean high water springs

To help identify mean high water springs you can:

• use lines on OS maps as a general guide
• use height data from the closest port and a ground level survey at the works site
• check the National tidal predictions for UK and Irish Ports
• use local figures commercially available for mean high water springs around Wales