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Our observations on the effects of hydrothermal runoff on fish in Yellowstone’s waters are unexpected. Studies show the maximum recommended temperature for trout is 68° F or 20°C, yet these fish occur throughout the Firehole River—even in places where the water temperature is much higher than that limit.

Also, the thermal waters dump arsenic and other elements into the water. Although arsenic is poisonous to humans, rainbow trout thrive in areas of the river with the most elevated levels! Brown trout are rare in such places so it’s possible these trout are more sensitive to certain elements or perhaps the temperature of the water deters them.

I bet that both the water temperature and its chemistry influence where different species of trout are best suited to live. I noticed there were few very young browns in the hottest parts of the river, so I suspect they don’t reproduce as well there—at least this is true for many fish in areas of thermal pollution.

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Cast of characters - Maya Crowbes, Dr. A Beadle, Gray Fischer, Viola DeRama
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Q: Can rainbow trout live in areas of the river with high levels of arsenic?