A pre-teen girl was preparing to go on a camping and fishing trip with her father and crazy uncle, the mother and brother staying back at the crazy uncle's house. The crazy uncle was more or less Doc from back to the future. There was something about sleeping one night in the crazy house he lived in, but I don't remember - in any case, the girl was excited to go camping rather than spend another night in the house. They weren't bringing much food, and she realized that that's because they would catch fish for dinner, which made her more excited (but her brother teased her about it, saying she was going to be living like a cave man or hobo or something along those lines).
The truck they took was full of unusual equipment, which the uncle set up once they got to the river. There was a bridge that was out. The girl soon found that she had a strange power to manipulate the river. She could make things happen by wishing. This was due to a combination of the uncle's machine and the favor of the river spirit. She tried asking for a bridge, and a bridge appeared, but it was built below the water rather than above it, so didn't look very useful. The uncle asked for the water to go down, which she granted, but she told him it was not a good idea because pushing so much water down took a lot of energy from his machine (she seemed very aware of the energy cost of different wishes); she said the machine would explode. The uncle didn't seem to take this seriously, but he soon realized that the lower water level meant the water wasn't serving as coolant for the machine and a key component would soon overheat (the name of the part was given, but I forget).
He sent her back to the house to get a replacement part. (It was not explained how she returned by herself.) She wouldn't say anything about the situation to her mother and brother. Her brother inferred that the camping was terrible, and said that he understood that her silence meant it was a hostage situation and that he'd get her out of it (and he said it so seriously that it wasn't clear whether he was teasing). There was something I can't logically fit in about her trying to communicate something with a drawing of a figure with yellow French-fry hair. Then I woke up.