Enter the island clue numbers in their cells — only some cells have numbers, the rest are blank. Then click Solve.
The solver expands each island from its clue cell (since islands can't touch each other), marks cells between two island clues as river, applies the no-2×2 rule, and then uses backtracking to fill remaining cells. All four rules are enforced: each island has exactly one clue; island size matches its number; all black cells form one connected river; no 2×2 area is entirely black.
Not sure what to enter? Click Sample to load a ready-made puzzle.
Shade a connected river around numbered islands — each island as big as its number.
The full guide, with a worked example and common mistakes: How to play Nurikabe.
Yes — only side-to-side contact is forbidden.
It is the rule that keeps the river narrow and the puzzle uniquely solvable.
Right-click or long-press a cell to mark it white (island). Click to shade it as river.