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Listen to Book 19: The River Expedition

All 150 answers from Book 19, read aloud. Press play and keep listening, or tap a question to jump to it. Each title links to its page with the video and the full answer.

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1.Where Does a River Begin?
2.What Is a Tributary?
3.What Is the Mouth of a River?
4.How Does a River Get Bigger as It Travels?
5.Why Do Mountain Streams Look So Fast and Big Rivers Look So Slow?
6.Which Rivers Are the Longest in the World?
7.Are Brooks, Creeks, and Rivers Different Things?
8.Why Are River Valleys Shaped Like a V in the Mountains but Wide Near the Sea?
9.How Does a River Carry Rocks and Sand Downstream?
10.Why Do Rivers Drop Sand and Pebbles When They Slow Down?
11.What Is a Watershed?
12.Where Does All the Mud Go at the End of a River?
13.What Happens Where a River Meets the Sea?
14.Why Does the Mackenzie River Run North Instead of South?
15.Why Do Some Rivers Split Into Many Weaving Channels?
16.Why Do People Argue About Where a River Really Starts?
17.How Old Are Rivers?
18.Why Does a River Sometimes Leave an Old Loop Behind as a Crescent-Shaped Lake?
19.Why Does River Water Turn White and Wild Over Rocks?
20.Where Does a River’s Water Come From When It Hasn’t Rained for Days?
21.Can a River Disappear Underground?
22.Why Do Some Rivers Have Different Names Along the Way?
23.Why Are River Rocks So Smooth and Round?
24.Where Does River Water Go After It Reaches the Sea?
25.How Can You Follow a Raindrop From Your Street to the Sea?
26.How Can You Tell How Fast a River Is Moving?
27.Why Does Water Move Fastest in the Middle of a River?
28.Why Does a River Dig Deeper on the Outside of a Bend?
29.What Are Riffles and Pools?
30.Why Does a River Bottom Have Ripples Like Little Sand Dunes?
31.What Do Ripples and Smooth Patches on a River’s Surface Tell You?
32.What Colors Can River Water Be, and What Do They Mean?
33.Why Are Some Rivers Milky Turquoise?
34.Why Do Some Rivers Look Dark Like Tea?
35.Is a River as Deep as It Looks?
36.What Does a Stream Gauge Do?
37.How Do Scientists Measure How Much Water a River Carries?
38.Why Does River Temperature Change During the Day and Seasons?
39.Why Do Some Rivers Have Foam on Top?
40.What Is an Eddy?
41.Can Scientists Listen to Rocks Rolling Along a River Bed?
42.What Can River Pebbles Tell Us About Upstream?
43.What Do the Layers in a Riverbank Tell Us?
44.What Is a Sandbar, and Why Does It Move?
45.How Do Scientists Follow River Water with Harmless Dye?
46.How Can You Read a River on a Map?
47.What Is a Seam, Where Fast and Slow Currents Meet?
48.How Do Whirling Pebbles Drill Holes in River Rock?
49.Why Does a Wave Stay in One Place While the River Rushes Through It?
50.How Do Scientists Map the Bottom of a River?
51.Why Do River Fish Face Upstream?
52.How Do Fish Hold Still in Fast Water?
53.What Lives Under the Rocks in a River?
54.How Do River Insects Breathe Underwater?
55.Why Do Mayflies Live Only a Day as Adults?
56.How Do River Bugs Cling to Rocks in a Strong Current?
57.Why Does Rushing Water Hold More Oxygen?
58.How Do River Otters Stay Warm and Dry in the Water?
59.Why Do River Insects Let Go and Drift Downstream at Night?
60.What Is a Dipper, the Bird That Walks Underwater?
61.How Does a Kingfisher Dive for a Snack?
62.How Do American Eels Swim From Rivers to the Faraway Sargasso Sea?
63.Why Do Salmon Swim Up Rivers?
64.How Do Young Fish Grow Up in a River?
65.Why Do Fish Leap Out of Rivers?
66.Can Dolphins Live in Fresh Water?
67.Why Do Frogs and Tadpoles Live in Quiet Corners of a River?
68.How Can River Plants Bend Without Breaking?
69.How Do Trees Along a Riverbank Help the Animals in the Water?
70.How Does a River Feed the Animals Along Its Banks?
71.Why Are Fallen Trees Good for a River?
72.Which Animals Wake Up Along a River at Night?
73.What Are Freshwater Mussels Doing on the Riverbed?
74.Why Do Sturgeon Look Like Dinosaurs?
75.How Do Animals Cross a Rushing River?
76.Why Did People Build Towns Next to Rivers?
77.How Did Rivers Become Highways?
78.Why Were Birchbark Canoes So Clever?
79.How Does a Paddle Move a Canoe Forward?
80.Why Do Flat-Bottomed Boats Work Well in Shallow Rivers?
81.How Can a Ferry Cross a River Without an Engine?
82.What Is a Ford, and Why Were Fords Important?
83.How Does a Canal Lock Lift a Boat Uphill?
84.How Is a Canal Different From a River?
85.How Did Boats Travel Upstream Before Engines?
86.How Did Paddlewheel Steamboats Work?
87.How Can a Barge Carry So Much?
88.How Do River Pilots Avoid Hidden Sandbars?
89.How Does a Water Wheel Turn?
90.How Did a Water Mill Grind Grain Into Flour?
91.How Does a Hydroelectric Dam Make Electricity?
92.What Are the Gates and Spillway on a Dam For?
93.How Do Fish Get Past a Dam?
94.How Did Loggers Float Trees Down Rivers?
95.How Does a Life Jacket Keep You Afloat?
96.How Can Ocean-Going Ships Sail Deep Inside a Continent?
97.What Is a River Port?
98.How Did Early Explorers Map Rivers?
99.What Is a Weir?
100.Why Are Many River Towns Built Above the Water, Not Right at the Edge?
101.Why Do Rivers Rise Every Spring?
102.Why Can a River Be High on a Sunny Day?
103.How Do Forecasters Know a River Is About to Flood?
104.What Does “Flood Stage” Mean?
105.Why Is the Land Near a River So Rich for Farming?
106.What Is a Levee?
107.Why Is Floodwater Stronger than It Looks?
108.Why Does Rain Run Off Pavement Faster than It Soaks Into Grass?
109.How Do Forests and Wetlands Slow Down a Rising River?
110.Why Do Rivers Get Smaller in Late Summer?
111.What Happens to River Animals When the Water Gets Low?
112.How Can You See a Drought in a River?
113.What Can a Dry Riverbed Tell Us?
114.Why Do Rivers Freeze Later than Ponds and Lakes?
115.Why Does Ice Grow Out From the Riverbank First?
116.What Is Frazil Ice?
117.Can Ice Grow on the Bottom of a River?
118.Why Does River Ice Boom and Groan?
119.How Can Ice Pile Up and Block a River in Spring?
120.What Is Spring Breakup on a Northern River?
121.Why Is River Ice Never Safe to Walk On?
122.How Do Fish Survive Under River Ice?
123.Can the Ocean Push a River Backward?
124.What Does a Flood Leave Behind?
125.How Can Scientists Tell How Big a Flood Was Long Ago?
126.What Makes a River Healthy?
127.Why Does a Clean River Have Lots of Different Bugs?
128.How Do Scientists Tell How Cloudy a River Is?
129.Why Does a River Need Oxygen?
130.What Does a Water Test Kit Check?
131.What Makes Green Slime Grow in a River?
132.How Do Detectives Find Where Pollution Is Entering a River?
133.How Does Litter Travel Down a River?
134.How Can a Water Wheel with Googly Eyes Clean a River?
135.How Can a Strip of Plants Catch Muddy Runoff Before It Reaches the River?
136.How Do Scientists Bring the Wiggles Back to a Straightened River?
137.How Do Scientists Count Fish They Can’t See?
138.How Can a Cup of River Water Tell Who Lives There?
139.How Do Satellites and Drones Watch a Whole River at Once?
140.How Do Sensors Keep Watch on a River Day and Night?
141.How Do Floating Trackers Show Where River Water Goes?
142.How Can Kids Help Look After a River?
143.What Jobs Do People Do with Rivers?
144.How Can Old Maps Show That a River Has Moved?
145.What Is a Rain Garden?
146.How Do Experienced Boaters Decide Whether a River Is Safe to Paddle?
147.How Does a River Help Clean Itself?
148.Are There Rivers on Other Worlds?
149.How Can You Safely Explore a River?
150.Which River Secrets Can Nobody Explain Yet?

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