What does it tell you about the water?

That the water is cold and clean. Brook trout cannot live in water that is warm or silted, so they leave a stream long before anything looks wrong to us. Finding one is the reading. Losing one is the warning.

• Field marksPale wormlike markings on the back. Red spots ringed in blue along the flank.
• SizeCommonly 15 to 25cm in small streams.
• WaterCold headwaters, Northeast
• Verified byA working naturalist. Named in full on the colophon.