One of your Pokemon has to learn surf.
Byron in Canalave City is the sixth gym leader in Pokemon Diamond. He specializes steel-type. His 3 pokemons are Bronzor, Steelix, and Bastiodon.
byron the sixth gym leader u fight him in canalave gym
the sixth gym is in canalave city
The Sixth Gym leader is Chuck, he has a Hiryama and a Poliwrath.
After you beat the sixth gym leader, you are allowed to use strength which moves the boulders.
The first gym in Pokemon diamond is in Oreburgh City
you need to use a strong fighting type like a lucario or medicham
The Pokémon the second Gym Leader has in "Diamond" are Cherubi, Turtwig and Roserade.
fire and ground
sixth gym laeder
The 6th gym leader is in Canalave City.
Step on the portals until you get to the gym leader.