Oranos. Only Major god with access to an aquatic myth unit in every age, also Sky Passages are a great way to move between islands.
Oceanus - Age 2 water myth unit to start the beats, Carnivora god power can be cast on water (right next to enemy dock) and gives you effectively 2 water myth units in classical. Caladria in the rear as an extra medic.
Losing Prometheus is sad, but winning the water in the 2nd age is worth it. Less Strong on Islands with large amounts of coast, but on a map like River Nile this is totally oppressive and game ending unless the enemy has some other way to cross the water.
Heroic Age gives a choice, Either go Hyperion and get Nereids and assume further control of the water, or go Theia for the Stymphalian Bird (viable on land and water) and better techs (especially Lemurian Descendants because LOS in a large water map is often hard to come by.)
Helios - Vortex lets you travel between islands without transports. Heka Gigantes are strong, but we're also getting a potential 3rd water myth unit in the Man O'War. Halo of the Sun buffs fire Siphon's
& SHIPS. Mirror Towers are another line of defense around your shoreline!
Out Reach
The guy who writes the erotic fan fiction in Yeebaagoon's signature