The key can be acquired by finding Lagos in the village of Wellgarth. Lagos is hiding in a secret passage within his prison cell. By probing the back of the cell, the secret entrance can be found. Lagos gives up the key when talked to by the heroes.
The Watergate Key has only 1 specific usage. It is used in Tuhn to open the watergate located in the northwest corner of town. Opening the watergate causes the river to flood, providing access by Ship to the Tower of the Moon.
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