Defining the Isles: What Really Makes an Island?

As part of the 4,000 Isles Project, a common question is: What exactly counts as an island? It’s more complex than it sounds.

The Core Criteria

Generally speaking, a UK island is:

• Surrounded by water at high tide
• Not attached to the mainland by permanent human-made infrastructure

But beyond this, there are several categories of islands:

• Tidal islands: Only islands when the tide is in (e.g. Lindisfarne, Burgh Island)
• Inhabited islands: With year-round residents (e.g. Mull, Yell, St. Mary’s)
• Remote or private islands: Often inaccessible or permission-only
• Freshwater islands: Found in lakes or rivers (e.g. Inchcailloch, Loch Lomond)

Walking across tidal sands to islands

How Are They Counted?

Scotland’s National Records count over 790 islands. The broader UK total (including estuary islands, lakes, and rock stacks) exceeds 4,000.

Why It Matters: Understanding how islands are defined helps shape the 4,000 Isles Project — and invites more people to explore the rich diversity of blue-space adventures across Britain.

Explore our full UK Island Map →

Your next island adventure awaits. Use these guides to plan your route, pack your kit, and explore slowly — one island at a time.

Visit our 4,000 Isles Project Page →

Scrambling up Asparagus Island, Cornwall