Great Whale enter the battlefield, their abilities trigger.
Resolve the
Shipwreck Dowser trigger, returning
Displace from your graveyard to your hand.
Resolve the
Great Whale trigger, untapping up to seven lands.
Repeat.
Notes
If you control seven lands that can tap to produce at least ({3} magic symbol) ({U} magic symbol) , this combo nets infinite mana, and you may blink any other permanent besides