Fold 1 First Reader
Swim, Otter, Swim!A river otter has webs.
The otter set
Six books about one animal. Each fold goes deeper than the one before, and every fact in all six comes from the same fact bank.
Watch a page grow up
Sea otters stay warm inside the thickest fur of any mammal. Drag the slider to read all six versions, word for word from the books, then try another fact.
Fold 2 Read Together
Hello, Otter!A river otter paddles with webbed feet. Its thick tail steers.
Fold 3 Early Reader
Otter: Life in the WaterRiver otters swim with webbed feet. A thick tail helps them go fast and steer.
Fold 4 Explorer
Otter: A Life in River and SeaA river otter swims with webbed feet and a muscular tail. Wide webbed paws paddle through rushing water. The thick tail acts like a rudder to steer.
Fold 5 Field Guide
Otter: A Field GuideRiver otters swim with webbed toes on all four feet and a thick, muscular tail that tapers to a point.
Fold 6 Deep Dive
Otters, Unfolded: The Science of River and SeaNorth American river otters swim with webbed feet and a thick, muscular tail. Webbing joins the toes on both front and hind feet, so each paw pushes against the water like a paddle. The tail makes up roughly a third of the body's length and works as a thruster at speed and a rudder in sharp turns.9
Fold 1 First Reader
Swim, Otter, Swim!An otter is not fat. It has lots of fur!
Fold 2 Read Together
Hello, Otter!Otters have no blubber. A sea otter has the thickest fur of any mammal.
Fold 3 Early Reader
Otter: Life in the WaterNo mammal has fur as thick as a sea otter's. Otters have no thick fat to fend off the chill.
Fold 4 Explorer
Otter: A Life in River and SeaUnlike seals, otters have no blubber to keep them warm. Instead, a sea otter has the thickest fur of any mammal on Earth.
Fold 5 Field Guide
Otter: A Field GuideSea otters have the thickest fur of any mammal on Earth, and because otters have no blubber, this dense coat is what keeps them warm in cold water.
Fold 6 Deep Dive
Otters, Unfolded: The Science of River and SeaSea otters have the thickest fur of any mammal on Earth, with up to one million hairs in a single square inch of skin. The coat traps a thin layer of air that keeps the skin dry in cold coastal seas. Because otters have no blubber, any break in this fur exposes the body directly to lethal heat loss.27
Fold 1 First Reader
Swim, Otter, Swim!An otter dips in. Yum!
Fold 2 Read Together
Hello, Otter!An otter holds its breath to dive for food. Its ears and nostrils close.
Fold 3 Early Reader
Otter: Life in the WaterAn otter shuts its ears and nose when it dives. Then it hunts in the water.
Fold 4 Explorer
Otter: A Life in River and SeaAn otter seals its ears and nostrils shut when it dives. Holding its breath, it hunts underwater for food. A sea otter usually stays down for one to two minutes.
Fold 5 Field Guide
Otter: A Field GuideSea otters and river otters both hold their breath to dive for food, and muscular valves seal their ears and nostrils shut the moment they go under.
Fold 6 Deep Dive
Otters, Unfolded: The Science of River and SeaOtters close their ears and nostrils when they dive for food. Muscular flaps seal both openings as the animal goes under, keeping water out of the airway and ear canals. Holding their breath, otters then hunt fish, crabs, and shellfish on the riverbed or the sea floor.45
Fold 1 First Reader
Swim, Otter, Swim!Lots of otters nap as one.
Fold 2 Read Together
Hello, Otter!A sea otter wraps in kelp so it won't drift away.
Fold 3 Early Reader
Otter: Life in the WaterSea otters rest side by side in a raft. An otter drapes kelp across its chest. Then it will not drift off as it naps.
Fold 4 Explorer
Otter: A Life in River and SeaSea otters wrap kelp around their bodies when they rest. Floating together in groups called rafts, the otters stay anchored against wind and currents.
Fold 5 Field Guide
Otter: A Field GuideResting sea otters wrap strands of kelp around their bodies so ocean currents do not carry them away, and they gather in floating groups called rafts.
Fold 6 Deep Dive
Otters, Unfolded: The Science of River and SeaSea otters wrap themselves in kelp to rest without drifting away. Floating on their backs, they drape fronds of giant or bull kelp across their bodies as an anchor against swell, wind, and tide. Sea otters also gather in floating groups called rafts to rest, groom, and sleep.69
Fold 1 First Reader
Swim, Otter, Swim!Some otters have a rock. Bam, bam!
Fold 2 Read Together
Hello, Otter!A sea otter uses a rock on its chest to crack shells.
Fold 3 Early Reader
Otter: Life in the WaterA sea otter sets a flat rock on its chest. It bangs shells on the rock to crack them. It tucks the rock in its skin pocket.
Fold 4 Explorer
Otter: A Life in River and SeaSea otters use flat stones as anvils on their chests to crack hard shells. A sea otter can tuck its stone into a skin pouch under its arm between dives.
Fold 5 Field Guide
Otter: A Field GuideSea otters float on their backs and crack hard shells against flat stones on their chests, tucking a stone into a skin pouch under one arm between dives.
Fold 6 Deep Dive
Otters, Unfolded: The Science of River and SeaSea otters use a stone on the chest as an anvil to crack open hard-shelled prey while they float on their backs. The otter hammers a clam, mussel, crab, or sea urchin against the rock until the shell breaks apart. Between dives, it keeps the stone and its catch in a loose pouch of skin under its arm.56
Fold 1 First Reader
Swim, Otter, Swim!Bad rivers do not have river otters.
Fold 2 Read Together
Hello, Otter!River otters need clean water. Where they live, the river is healthy.
Fold 3 Early Reader
Otter: Life in the WaterRiver otters must have clean water with lots of fish. Sea otters do well where the sea is kept safe.
Fold 4 Explorer
Otter: A Life in River and SeaRiver otters need clean water, so river otters are a sign of a healthy river. Sea otters thrive in protected ocean areas with plenty of food.
Fold 5 Field Guide
Otter: A Field GuideRiver otters are bioindicators whose presence signals clean fresh water, and along the California coast, marine protected areas give sea otters safe havens with plenty of prey.
Fold 6 Deep Dive
Otters, Unfolded: The Science of River and SeaRiver otters signal clean water, because they sit high in freshwater food webs and vanish quickly from polluted streams; their presence therefore marks a healthy watershed. For sea otters, networks of coastal marine protected areas limit fishing gear, protect kelp canopies, and prevent disturbance, giving them safe havens with abundant prey.92
The facts behind it: A river otter has webbed toes and strong claws on all four feet. A river otter propels and steers with its thick, muscular tail. 3 published sources
The facts behind it: A sea otter has the thickest fur of any mammal on Earth. Otters have no blubber to keep them warm. 3 published sources
The facts behind it: An otter's ears and nostrils seal tightly shut underwater. An otter holds its breath to dive for food. 4 published sources
The facts behind it: A sea otter wraps itself in kelp to float safely. Sea otters rest together in floating groups called rafts. 4 published sources
The facts behind it: A sea otter uses a rock on its chest to crack open shells. A sea otter has a loose skin pocket under each arm to hold food and tools. 3 published sources
The facts behind it: River otters are bioindicators whose presence signals clean freshwater ecosystems. Marine protected areas give sea otters safe havens with abundant prey to rebuild populations. 4 published sources
Fold 1 · First Reader · Tide pool
Swim, Otter, Swim!
- Ages
- 4–6
- Trim
- 6 × 9 in
- Pages
- 24
- Words
- 108
Meet river otters and sea otters as they zig, zag, dip, nap and crack shells on a rock. Every word of the story is a short sound-it-out word, a common sight word, or one of four pictured words (otter, river, fur, rock) taught on page 3, written for a beginning reader to read alone. Notes for grown-ups at the back give the facts and sources.
Fold 2 · Read Together · Sunlit shallows
Hello, Otter!
- Ages
- 6–8
- Trim
- 8.5 × 8.5 in
- Pages
- 32
- Words
- 256
Can you kick your feet like a river otter? Can you hug yourself warm? Read along with Nina and Theo as river otters slide down muddy banks and sea otters wrap up in kelp, crack shells on a rock and carry their fluffy pups. Short questions and splashing sounds give children a part in the reading while an adult reads aloud. Notes at the back explain the fact behind each picture and name their sources.
Fold 3 · Early Reader · Coral reef
OtterLife in the Water
- Ages
- 8–10
- Trim
- 6 × 9 in
- Pages
- 32
- Words
- 534
Meet river otters and sea otters as they swim, dive, slide and crack shells. Short sentences, big pictures and three pictured words help children who are ready to read on their own. Includes a short quiz and the six facts shared across the series.
Fold 4 · Explorer · Kelp forest
OtterA Life in River and Sea
- Ages
- 10–12
- Trim
- 8 × 10 in
- Pages
- 40
- Words
- 2,123
Why does a sea otter wrap itself in kelp to sleep? How can an otter stay warm with no blubber? Five chapters follow two otters: river otters sliding down muddy banks and sea otters cracking shells on stone anvils. Seven labeled diagrams, Wow! boxes, a quiz and a glossary help along the way, with questions from Nina and Theo. Every fact was checked against published sources.
Fold 5 · Field Guide · Open ocean
OtterA Field Guide
- Ages
- 12+
- Trim
- 8 × 10 in
- Pages
- 48
- Words
- 4,529
Otter: A Field Guide compares two otters: the North American river otter of streams and lakes and the sea otter of the North Pacific coast. Learn how dense fur and a fast metabolism keep otters warm without blubber, why sea otters crack shells on stones balanced on their chests, and how river otters signal clean water. Six chapters, seven diagrams, field notes from Nina and Theo, Try it and Scientist spotlight boxes, a glossary, and a full list of sources.
Fold 6 · Deep Dive · The deep
Otters, UnfoldedThe Science of River and Sea
- Ages
- 12+
- Trim
- 6 × 9 in
- Pages
- 58
- Words
- 7,296
River and sea otters took very different paths back to the water. Follow those paths through the physics of the densest fur of any mammal, the mechanics of breath-hold diving, stone-tool traditions learned mostly from mothers, the power of a keystone predator in the kelp forest, and the recovery of a species hunted to fewer than 2,000 animals. Six connected chapters draw on published research, with numbered endnotes, a list of references, and an index.
First edition, 2026. Printed on demand as premium-color paperbacks. See every fact they use