Out of Reach

Easy Used by Smart Hint

A cell too far from every remaining clue for that island to ever stretch to — it's sea.

Sea
Cells that establish the pattern
Where the conclusion lands

How it works

This clue needs just one more cell, so its island can only ever reach its own immediate neighbors.
A cell this far away — checked against every remaining clue on the board, not just this one — can never be reached by any of them. It's sea.