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Diadromous fish migrate from the sea to fresh water in order to spawn. When the migration route has been blocked (due to a man-made dam or other barrier), structures called fish ladders can be constructed to help the fish complete their journey.

In these puzzles, you will design a fish ladder using large, pre-cast columns. These steel-reinforced concrete columns can be stacked one on top of another if necessary, but cannot be cut.

In the completed ladder, the water level must step down in one-foot increments. (The horizontal lines on the figure and in the columns indicate these one-foot increments.) The columns can only be inserted at the locations marked by the red dots. You may not need to use all of the columns provided.


Fish Ladder Example

Because there is a two-foot difference between the water levels at the highest and lowest barriers, you must add one barrier to break that drop into one-foot steps. Depending on whether you had a column of height three, four, or five feet, you would use one of these solutions:

Fish Ladder Example Solution A

Fish Ladder Example Solution B

Fish Ladder Example Solution C

solving tips

Keep in mind exactly how many and what type of columns you are given to solve each puzzle. For instance, if you are only given three-foot and four-foot columns, then there is no way that you can make a five-foot column. As another example, if you are only given one four-foot column, you may want to try to determine where that column must be placed.