ok, how about mudkip (evolves into swampert = water/ground)
a dual water type thats good against other water? id say lanturn. EV train it in sp atk and speed, teach it some special electric and power up moves, and you should be good to go. i can try and get one for you if you want me to.
EDIT: come to think of it, Ludicolo might be a better choice, with it being half grass, and can take out pokemon like swampert and whiscash with 4x damage, while lanturn can't even touch it... but i can't get lotad because i don't have sapphire to dual slot catch it