"Goes Upstream" is the eighth episode of season three and the thirty-fourth episode overall of the animated children's series The Magic School Bus. It originally aired on November 2nd, 1996.
Ralphie is in charge of bringing the fish for the school's Fish Fry, but unfortunately, there are no salmon in the spot he usually fishes with his uncle. Ms. Frizzle takes the class on a field trip to find out where the salmon are and changes the bus in to a migrating salmon. Eventually, they find them, the class becoming salmon themselves. Not wanting to disturb them, they bring fish-shaped potatos to the fry instead.
The class is going on a fishing trip and Ralphie is perplexed over the paucity of salmon in the sea. The class has yet to catch a single fish and they won't have anything to searve at the all school Fish Fry. Just then, Ralphie catches a bite and reels it in, only to find that it is Ms. Frizzle dressed in a fish suit. When Ralphie tells the teacher about the dearth amount of fish the class has caught, Ms. Frizzle guides the class inside the bus and Liz transforms the bus into a salmon right before diving underwater. Ms. Frizzle uses a microbus software disk as a brain for the salmon to have the bus think like a salmon to put inside the software. the bus is also replete with microbus window, which lets the class see what the bus is thinking, which shows that it is going to eat more of the fish underwater. The class is engrossed when they see other thought of the bus and Arnold comes across a pressure sensor, which lets the others know what to watch out for using the water pressure. Just then, the bus comes across the shark and Ralphie attempts to steer, only to learn that the bus has a mind of its own and thinks on its own. It narrowly avoids the shark and comes across more fish. To the class' surprise, they find that the bus isn't hungry anymore and it comes across more salmon. Ralphie then changes his mind and wants to go back. Dorothy Ann then reads up into her book that when a salmon loses its appetite and starts joining the other salmon going into the same direction, the salmon are migrating, and the class wonders where the bus is going.
D.A. reads in her book that animals who migrate travel up to 1,000 miles and could take months. Ralphie then has a plan to turn the bus around outside. Ms. Frizzle offers the class diver suits to swim underwater (with Phoebe, D.A, Arnold, and Tim still inside the bus) and get the bus to turn around. But the bus continues swimming and Arnold discovers that the water is losing its salt according to the bus, meaning that the bus is no longer swimming in the ocean anymore. Tim surmises that the bus is swimming through the river, and D.A. explains that salt water fish die in fresh water. Ms. Frizzle tells the class that salmons are versatile and can switch from being salt water to fresh water fish.
Meanwhile, Ralphie, Carlos, Keesha, and Wanda are riding onto each of the four salmons and find that the bus has stopped and is surrounded by other salmon. When they notice that the salmon are gradually changing appearances, Ms. Frizzle explains that salmon change in fish years and are also waiting for the water to rise since the river is low and hardly any water comes down. Just then, a thunder storm comes down and the salmon continue to migrate.
When the storm ends, the four students hide behind the seaweed on the land and Ralphie decides to use Caviar Alamode, a fisherman, to catch the salmon-transformed bus. They grab onto the hook he casts over his shoulder and end up into the river. The bus hooks onto the bait and is reeled in, only to later release itself off. The students inside the bus discover the smell inside and try to figure out where it is coming from, as well as the puzzle coming together.
Meanwhile, the four students outside come up with a plan to lure the bus to the waterfalls since it wouldn't make it through the dam. To there surprise, however, the salmon hop over the dam and above the moving stream overhead. Inside the bus, Arnold learns that the bus has stopped moving and that the picture is now complete. Ms. Frizzle tells the class that it is now the destination for the bus and the rest of the salmon. The other four students outside swim to the bus' destination and make it inside. Ms. Frizzle ejects the disk out if the software and adds in another disk, which causes the class to end up in each egg the bus laid and inside the underwater stream with the rest of the laid eggs.
While inside the eggs, the class learns that salmon migrate to find their place to laid their eggs, which is why the females migrate. When Tim asks why males migrate, the class learns that males do it to fertilize the eggs hatching. Ms. Frizzle lets Liz, suited in a wetsuit, out of the bus, which buries the eggs with rocks. The bus shines on the eggs and the class hatch out of their eggs as baby salmon. They search for food and eat the fish food Ms. Frizzle offers them. They then grow a bit bigger and congratulates the bus for helping them learn migration. Ms. Frizzle exits the bus wearing a wetsuit and tells the class to think like a salmon to guess how a salmon would know about a river and be able to find it. The class then learns that salmon follow the smell of the place they once grew up in and migrate to it, giving their progeny a chance of survival. Ms. Frizzle also adds that although little streams are good for little salmon, the ocean is much ample for bigger salmon. So the class enters the bus, which transforms into a duck and flies away.
At the all school Fish Fry, the class returns with potato French fries and tells Janet about the migration of the salmon, who they decided to let be. Ms. Frizzle adds, "Once you've seen the salmon on the move, the rest is potatoes" (from her friend Astergen General), which evokes laughter from the other class.
- Janet makes her fourth appearance at the end of this episode.