Marine licensing - Definitions

This guidance provides definitions for some commonly-used terms on the subject of marine licensing.

Applies to England and Northern Ireland


The Marine Management Organisation (MMO) is responsible for marine licensing in English inshore and offshore waters and for Northern Ireland offshore waters.

MMO Jurisdiction (1)

‘English waters’ is the area of sea within the limits of territorial waters (12 nautical miles) adjacent to the English coastline (the ‘inshore’ area). This also includes any area of sea beyond the territorial limit (the ‘offshore’ area), that is within the exclusive economic zone (EEZ) and the UK sector of the continental shelf (up to 200 nautical miles). This excludes the waters of any devolved administration.

‘Northern Ireland offshore waters’ is the area of sea, adjacent to Northern Ireland beyond the territorial limit, providing it includes the EEZ and the UK sector of the continental shelf (excluding the waters of any other administration).

MMO Jurisdiction (1)

Mean High Water Springs

Monthly tides are defined as ‘Springs’ or ‘Spring tides’ when the tidal range is at its highest and ‘Neaps’ or ‘Neap tides’ when the tidal range is at its lowest. The height of Mean High Water Springs (MHWS) is the average throughout the year, 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).

Mean High Water Springs (1)

Most potential applicants will find it difficult to accurately identify MHWS without specialist equipment. The MMO therefore recommends that potential applicants err on the side of caution and treat an area as being below MHWS if it is made wet from the normal ebb and flow of the tide or if there is evidence such as marking or growth that would suggested the tide has reached a point in the past.

If you remain unsure we advise that you undertake an independent survey to confirm the position.

Normal Tidal Limit

The Normal Tidal Limit (NTL) is the extent to which a body of water is affected by the ebb and flow of the tides. This may encompass rivers and their estuaries, including those areas that are controlled by locks.

Mean High Water Springs (2)

What do we mean by ‘The Sea’?

‘Sea’ includes any area which is submerged at MHWS and the waters of every estuary, river or channel where the tide flows at mean high water spring tide up to the NTL.

Even waters in areas which are closed permanently or intermittently by a lock or other artificial means against the regular action of the tide are included, where seawater flows into or out from the area, either continuously or from time to time.

In or over the sea, on or under the seabed

‘In’ the sea includes a location within any relevant body of water.

‘Over’ the sea includes a location directly above or overhanging the sea such as a bridge, open piled structure or cantilever.

‘Seabed’ includes the ground under the sea and includes anything resting on it such as a wreck.

In or On the sea, On or Under the Sea Bed

Anywhere else in the world

The MMO is also responsible for marine licensing in other parts of the world in certain circumstances where the activity undertaken involves:

If you intend to carry out any of these activities in another part of the world, select the relevant activity for more information.

Published 30 May 2019