Instant, U (1)
Common (C1)
Until end of turn, whenever a player taps an Island for mana, that player adds {U} to his or her mana pool (in addition to the mana the land produces).
"By the time their enemies noticed the sea's changing mood, the Vodalians had often shifted formation and were ready to attack."
—Sarpadian Empires, vol. V
Illus. Amy Weber

3/1/2010: The delayed triggered ability triggers and produces {U} any time a land with the land-type Island is tapped for mana, even if that land has other types or the mana for which it was tapped is another color. For example, if you tap a Breeding Pool for {G}, High Tide will give you an extra {U}.
3/1/2010: The effect applies even if the Island in question entered the battlefield after High Tide resolved.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander