Gush travels with the kids to the Arctic Ocean to finally find the mysterious "horned whale," which has eluded him for a long time. As it turns out, what they see is not really a "horned whale," but a narwhal. / After hearing that a great white shark has a toothache, Splash and friends enlist Denny to help, not realizing that in the world of cleaner shrimp cleaning the teeth of the great white shark is a revered accomplishment.

When Splash and Bubbles hear that one of Ripple's Brothers has wandered off, they join Ripple's search, while enlisting the help of Zee and her new friend, Hamilton the hammerhead shark, to find him. / Maury discovers Denny's molted exoskeleton in the reef and assumes something must be wrong with "the real Denny," so he enlists the help of Splash and friends to find her, only to discover that she has simply molted.

Mayor Sting has to attend a stingray migration, which will take him away from the reef. Dunk volunteers to fill in as the mayor for the day, thinking it will be an easy job, but has no idea what it takes to keep the reef thriving and safe. / When Bubbles goes looking for the ultimate mud puddle, she ventures down to the Deep, where Lu takes them to see a hydrothermal vent and meet some lipstick tubeworms and Oblo the blobfish.

The Reeftown Rangers wonder where the end of the ocean is, or if the ocean even has an end. They venture out to find the end of the ocean and discover a rainbow salmon, Sal, who teaches them about the difference between fresh water and seawater, and about where all the water goes beyond the ocean. / Splash, Bubbles, Dunk and Ripple travel to the Antarctic and meet a new friend, Dive, a gentoo penguin who can live in and out of the water. Dive wants to be a Reeftown Ranger, but needs to learn that he is not just like a fish!

When Splash and his friends are playing at the sandy bed, they find a parrotfish munching on some coral and helping to create the sandy bed on which they're playing, because parrotfish produce sand from their bodies after they eat. / When Bubbles gets trapped in a treasure chest, Splash and his friends can't get her out. Luckily she's not alone when they discover Wave in there, who they think is also stuck until he show that being an invertebrate means he can squeeze even tiny spaces.

When Lu's light goes out, Lu has trouble attracting food and seeing down in the Deep, so the kids decide to show her a world filled with light - the reef. There they realize that Lu's light didn't go out, it's just covered with mud. / On a sleepover with Zee, Bubbles is fascinated to learn that Zee is nocturnal. Zee can't help it, she goes out to play and look for food at night! Bubbles is so excited about this new discovery that she tries to stay up with Zee to learn about and explore what it's like to be nocturnal.

The Reeftown friends arrive at the Arctic, where they don't find Melody, but instead meet Whistler, a narwhal who is a very unique creature with many interesting attributes, including a tusk on his head. / The kids finally find Melody just in time to see her at the krill bloom, where they learn all about the food chain going from the tiny krill all the way up to the huge whale. Their journey ends by hearing the beautiful music of the humpback whale before returning home to Reeftown.

Chompy the Parrotfish decides she doesn't want to eat only algae anymore when she sees Splash and his friends eating a variety of things found in the water column (plankton, etc.) The others have to get Chompy back on her normal eating plan before the reef gets overrun with algae! / Bubbles and Ripple meet a jellyfish. However, when they bring Splash and Dunk to meet her, they discover she doesn't remember them at all. The kids learn that what they thought was one jellyfish were actually two identical clones of each other.

When a big storm passes over Reeftown, the friends experience rain and stormy conditions. They learn they don't need to be afraid, but it's good to stay close to home in a storm and take shelter. / The kids' old friend Scoot, a juvenile sea turtle, stops by the reef to see Splash and the gang. While there, he explains that he is getting older and wants to scout for some potential places to settle, so the kids show him everything that Reeftown has to offer!

While playing, Splash senses something is wrong and quickly swims out of Dunk's way as he comes in for a hard landing. The strange thing is that Splash wasn't even looking in Dunk's direction, so how did he know he was coming? Convinced that he has some sort of superpower, the kids begin testing Splash's limits in a series of sneak attacks, which never work. Gush soon explains that Splash isn't a superhero, but simply has a lateral line sense, which is common for fish. / Ripple feels like she is struggling to be part of her group of friends, then meets a shy oyster named Pearlene, who also feels isolated from those around her. Seeing how nice and kind Pearlene truly is, Ripple encourages her to "open up" to others and make new friends. She does, and finds that, despite her rocky, mucky exterior, she has a great inner beauty: not just the pearl inside of her shell, but also her warmth and compassion for everyone.

Dunk meets Puffy, a female pufferfish who admires his sand patterns, and becomes friends with her. When he starts spending all his time with just Puffy and not with the group, the gang teaches Dunk that it's good to make new friends, but keep the old ones as well. / When Splash experiences his first earthquake on the reef, Bubbles and Dunk decide to go on a quest to find out what causes "the big shake" and help put their friend's mind at ease.

Splash, Dunk and Bubbles try to help a fish that they've never seen before find out who it is and where its home is. / When Splash joins Bubbles, Dunk, and Ripple for a sleepover in the Sandy Bed, they discover that Splash doesn't sleep much; after unsuccessfully trying to help him, they learn that "schooling fish" don't need as much sleep.

After putting some Asterina starfish in the Kelp Forest where they don't belong, Splash, Ripple, and Tidy must get rid of them before the starfish eat all of the kelp. / Dunk, Bubbles, and Ripple don't believe Splash when he tells them about a mountain that spits out fire that can be found in the water really far down in the deep. To solve this mystery, the kids find Lu, who takes them into the deep to find a submarine volcano.

The Reeftown friends arrive at the Arctic, where they don't find Melody, but instead meet Whistler, a narwhal who is a very unique creature with many interesting attributes, including a tusk on his head. / The kids finally find Melody just in time to see her at the krill bloom, where they learn all about the food chain going from the tiny krill all the way up to the huge whale. Their journey ends by hearing the beautiful music of the humpback whale before returning home to Reeftown.

When Splash invites Ripple, Bubbles and Dunk on a Reeftown Rangers exploration adventure, the friends worry that Splash will find another home out there in the big ocean and move on from Reeftown. / Splash and his friends meet Scoot, a young sea turtle who is riding the currents. As Reeftown Rangers, the group wants to help the mischievous turtle on his journey and see some new places along the way!

Still traveling with Scoot and looking for Flo's home beach, Splash recalls hearing about a beautiful reef nearby - perhaps that's where Flo's home is. They're all surprised when the once lush reef turns out to have become a ghost reef. Splash and friends, as Reeftown Rangers, stay to help the one remaining Parrotfish save the reef, realizing that if harm can come to this reef, it can happen to any reef, including Reeftown. / Splash and his friends end their journey, returning home to Reeftown, where they are delighted to see that Splash now knows that although there are fun adventures to be found all over their "One Big Ocean," Reeftown is home to him.

Splash and Bubbles have an argument and decide not to play together for a while. With the help of Dunk and Ripple, they learn how much better things go for each of them when they communicate and cooperate. Splash's friends think he is so good at hide and seek that they decide to challenge him to find sea creatures who can blend into the background, making them very hard to find.

The Reeftown Rangers discover that, unlike them, Melody the fin whale migrates twice a year to follow the krill. Inspired by Melody, Splash and the others attempt to experience migration for themselves, beginning in the Antarctic, where they meet Mac, a mackerel icefish. / The Reeftown Rangers, continuing their migration adventure in the Antarctic, meet Pebbles, a gentoo penguin, and learn that she will receive a gift of a pebble from a male penguin who wants her to be his partner for life.

When Splash and his friends are playing "surprise fish," they accidentally release a "fear smell alarm," which spreads from fish to fish and causes Mayor Sting to call for everyone to be "reef ready!" / The Reeftown Rangers help Dorsal locate his old friend Spin, another spinner dolphin who he hasn't seen since he was young. They recognize each other with their unique whistle names and are happy to be reunited after many years.

Splash and Bubbles stop to visit Tidy for the day, but find him exhausted from constantly cleaning up behind the new kelp forest resident, Tyke, a young female Pacific harbor seal pup. Splash and Bubbles try to help Tidy by seal-sitting the young seal pup, and quickly learn how hard it is to keep track of their curious and fearless new mammal friend. / Splash and Bubbles realize that Zee is alone on the reef as the only shark, but when they learn that she has a distant relative in Reeftown, Zee is excited to discover who it is.

Splash and friends are playing in their clubhouse when Jerome and the fusiliers show up, claiming that the ship is actually their clubhouse. The two groups must then figure out who can use the clubhouse once and for all. / Being the newest member of Reeftown, Splash discovers the majority of things around him on the reef are actually living creatures. Some corals, some spongy things, some creatures he had no idea about, but no matter what their size, color or shape, he finds out that each have their own unique voice to be heard!

Splash and Bubbles stop to visit Tidy for the day, but find him exhausted from constantly cleaning up behind the new kelp forest resident, Tyke, a young female Pacific harbor seal pup. Splash and Bubbles try to help Tidy by seal-sitting the young seal pup, and quickly learn how hard it is to keep track of their curious and fearless new mammal friend. / Splash and Bubbles realize that Zee is alone on the reef as the only shark, but when they learn that she has a distant relative in Reeftown, Zee is excited to discover who it is.

Splash takes his pals to go see his friend, LU, a fearless explorer in the deep. He has met Lu in his travels, and she has been an inspiration for Splash. Lu turns out to be a female football fish (the "Lu" stands for "bio-LU-minescent") who leads them on an adventure in the abyss. / Wave, the octopus, loves the musicality of Reeftown, but tries to keep others from discovering that he has no rhythm.

While playing in the kelp forest, Splash, Bubbles and Dunk meet Tidy the Garibaldi Fish, who is the self-appointed Kelp Forest Ranger. Tidy has been taking the kids' shells as they play in the forest, because he likes to keep everything clean and tidy. / Bubbles injures her fin and has trouble swimming, but still wants to move around, so she begins trying all of the methods that other creatures on the reef use to move.

Ripple is excited because, according to legend, tonight is the night that Whitebeard, a mysterious creature who lives in the North Pole, sails over Reeftown, singing his beautiful music. She tries to convince the other Reeftown friends to stay up and watch for him to appear. / It's the holiday season in Reeftown as everyone gets ready for Coral Day, a celebration of the wonderful coral that make up their home. Splash, new to Reeftown and its traditions, wonders what he can contribute to the festival.

Splash sees a beautiful fish go by and instantly wants to be its friend, but whenever he tries to talk to the fish, it ignores him. He and his friends soon learn the fish has false eyespots on her back and had no idea they were trying to talk to her. / When Finny, a green dragonet, joins the group to play one day, Bubbles starts to worry that they're so similar, her friends won't need her around anymore.

The kids find a tooth lying in the sand outside the reef, and they are determined to return it to the owner, even when they find out it's a shark! / Splash and his friends have a race around the reef, and Splash wins by riding the currents instead of swimming. Bubbles and Dunk then want to know all about the currents so they too can race faster.

Dunk discovers that what he considers "just playing with sand" is actually considered beautiful art by his friends, and he is proud of himself for having a special talent. / Ripple leads the gang to investigate the legend of the Sea Dragon that has been passed down in her family. When they discover what Sea Dragons actually are, they learn that just because they haven't seen something before doesn't mean it doesn't exist.