Introducing Aquarium, a New Water Level Logic Puzzle on Puzzle Lair

We just added another puzzle type to Puzzle Lair, and it brings a calm, spatial kind of deduction to the site. Say hello to Aquarium, a logic puzzle for players who enjoy reading grid clues, thinking about how pieces fit together, and letting one small deduction cascade across the whole board.

What Is Aquarium?

Aquarium is played on a grid divided into bold-outlined regions called aquariums. Your job is to decide how high the water sits in each aquarium so that every row and every column holds exactly the number of water cells printed along its edge.

Two physical rules govern how the water behaves:

• Level. Within a single aquarium, a row is either entirely water or entirely dry, never partly filled, even when the aquarium bends or splits into separate arms.
• Gravity. Water fills an aquarium from the bottom up, so a water cell always has water beneath it in the same aquarium.

Together these rules mean every aquarium has just one degree of freedom, its water height, whether it fills three rows, one row, or stays completely empty. The numbers along the top and side of the grid count water cells, exactly like a row or column total. A clue of 0 means that whole line is dry. A clue equal to the line length means every cell is water. Everything in between is where the puzzle lives.

How to Solve It

Start with the clues that only one height can satisfy. If an aquarium is the only one occupying a row or column, or if the arithmetic only works one way, its height is fixed immediately. Small aquariums and short lines are the easiest places to find these direct hits. Once a height is pinned, mark every cell it implies. A fully dry aquarium clears all of its cells at once, and a fully flooded one fills them all, either of which often finishes the clue for that line.

When no single clue settles a height, cross-reference. Compare a row against the columns that cross it, and if a height forced in one line would push a crossing line's clue too high or too low, that height is ruled out. Working a clue from both directions at once is how most Aquarium deductions actually land.

Height limits round out the toolkit. An aquarium can never hold more water than the rows it spans, so a clue that looks generous is sometimes impossible for a short aquarium to reach on its own. When an aquarium is too short to satisfy a clue by itself, its top rows stay dry no matter what, and you can exclude water there right away. Every Puzzle Lair Aquarium puzzle is guaranteed solvable by logic alone, so if you are stuck there is always a deduction waiting, never a guess.

Why We Built It

Aquarium has a different solving rhythm from the number puzzles on Puzzle Lair. There is no arithmetic to grind through and no digits to track. Instead you are reasoning about shape and level, reading a clue as a question about how the aquariums crossing that line divide up its water.

We wanted a puzzle that feels gentle and visual at first, but rewards patient cross-referencing as the grid grows. Easy puzzles give you a quick introduction with roomy regions and short lines. Medium and hard puzzles pack in more, smaller aquariums, which sounds easier but is actually where the real deduction hides, since each region touches more lines and constrains more of the board.

Try It Now

Aquarium is live on Puzzle Lair today, with easy, medium, and hard difficulties to work through. It supports both Check mode and Instant mode, so you can fill and clear water freely and press Check when you think every aquarium sits at its correct level, or switch to Instant mode to have wrong water flagged the moment you place it.

Aquarium is launching in beta while we tune the puzzle generation and difficulty balance, so if you run into anything unexpected while playing, we would love to hear about it.

Head to the Aquarium puzzles and give it a try. If you like logic puzzles that reward careful reading and steady, guess-free deduction, this one should give you plenty to think about.