You can only activate 1 card with this card’s name per turn.
(1) Send 1 face-up “Umi” you control to the GY; you cannot Special Summon monsters until the end of your next turn, except WATER monsters, also Special Summon up to 2 WATER Normal Monsters, and/or monsters that specifically list “Umi” in their text, with different names from your hand or Deck in Defense Position, then, if your opponent controls a monster, you can Special Summon any number of Level 6 or lower WATER Normal Monsters from your hand or Deck.