This means you haven't learned to surf yet.
You can just use a strange power or surf to get out of it. If you load up, if you can't pass, it means you haven't learned surfing yet. You have to go there first. at your father's gym only after beating him.
After surfing (or after completing the level), the leader of the Silverleaf Electricity Gym will stand in the middle of the city and have a conversation. He will give you the key to the power plant and ask you to do it. go to the power plant and turn off the switch. Exit the city from the bottom. There is an island to the right of the water that appears. Enter the power plant.