Legendary Duelists: Duels from the Deep gave the Umi series its boss monster in the form of the attributal floodgate that is Ocean Dragon Lord - Kairyu-Shin , this together with A Legendary Ocean are the main cards you want to see in your hand, the later being able to be searched via Warrior of Atlantis , Terraforming and Ocean Dragon Lord - Kairyu-Shin , Kairyu can also search the insane Fish Sonar that basically searches most of your monsters, you can also use the Omni-negate Electric Jellyfish 's effect to send your Umi and retrieve it with Yorishiro of the Aqua 's GY effect.
Infernalqueen Salmon is also an important card in the deck since this fiendish fish can summon from aynwhere her husband Terrorking Salmon which under A Legendary Ocean means you get a free R4NK like Bahamut Shark into Toadally Awesome or Number 4: Stealth Kragen , Doom Kraken also helps since he can bounce one water monster you control to dodge negates or just re-add to your hand your Queen so you can summon another King next turn. Dream Shark also helps when making R4NKs since its a LV5 that special summons itself if you control a water monster.
Kashtira Ogre is here to give you a free body and banish, Mega Fortress Whale can bombard your opponent's monsters during your battle phase which is also an important aspect of this deck Sea Stealth Attack and Sea Stealth II ,the original one protects your S/T and destroys monsters your waters battle with, while II allows you to summon from hand or grave any water allowing you to bounce with Doom Kraken or Pop with Whale.
Kairyu-Shin's Dark Reef can send your Sea stealths too to summon 2 monsters that list Umi, Rage of Kairyu-Shin pops and disables monsters zones, it should be noted this card can block the extra monster zone killing most link decks (which should be happening if you have your flood [ignore that marincess exists, they arent real and cant hurt you]), the deck can also play under There Can Be Only One and Gozen Match . It should also be noted that Pacifis, the Phantasm City is good in the mirror match, but that means you can only run 2 legendary ocean which means you will be stuck with unsummunable monsters.
There arent that many combos in the deck since most of it is improvisation, you will be putting resources to get Kairyu and Umi on the field as quickly as possilbe.