The last starter monotype! Water's so versatile and diverse. I'm a huge fan of the Water/Ground dual type, but I won't overload on this team (but I bet you know which one I'm including...):
Gyarados @ Muscle Band
Adamant Nature, 252 EVs in Spd and Atk, 6 in SpDef (just because anything helps to guard against random Thunderbolts)
- Dragon Dance
- Earthquake
- Waterfall
- Return
I stayed away from Rain Dance just because you don't need to tempt any Thunderdancers out
Lapras @ Leftovers
Modest Nature, 252 EVs in SpAtk and Def, 6 in SpDef
- Surf
- Ice Beam
- Thunderbolt
- Confuse Ray
Lanturn @ Damp Rock (MUST HAVE VOLT ABSORB ABILITY!)
Bold Nature, 252 EVs in SpAtk and HP, 6 in Def
- Rain Dance
- Surf
- Thunder
- Signal Beam
Starmie @ Wise Glasses
Modest Nature, 252 EVs in SpAtk and Spd, 6 in SpDef
- Surf
- Psychic
- Ice Beam
- Rapid Spin
Tentacruel @ Black Sludge
Calm Nature, 252 EVs in Def and SpDef, 6 in HP
- Toxic
- Barrier
- Surf
- Confuse Ray
And last, but certainly never least...
Swampert @ Expert Belt
Hasty Nature, 252 EVs in Spd, 128 in Atk and SpAtk
- Surf
- Ice Beam
- Earthquake
- Brick Break
Any thoughts, comments or critiques?