Research locates cold-water areas crucial for fish survival
Last updated 11/17/2021 at 1:09pm
To humans, rivers in the Methow can seem pretty frigid, even in August. But for fish in the Methow, having cold water – really cold – is a matter of life and death.
Aquatic ecologist John Crandall has been walking along the rivers in the Methow watershed – the Methow, Chewuch and Twisp – with an elongated thermometer, taking the water temperature as he goes.
Crandall isn't wandering at random. He's following color-coded maps based on thermal imagery taken with an infrared camera from helicopter flights in 2009. The maps show all three rivers, small streams and tributaries, which are shaded from gold to hot pink, to purple, blue and black. Gold areas are the warmest, purple and blue are cold, and black is the coldest.
"It's just like being a pirate going out to find treasure. The 2009 flight data are my map," Crandall said.
On the detailed maps, much of the mainstem river is colored yellow or orange, about 17 to 10 degrees Celsius. But there are precious little pools of indigo surrounded by purple and red, more than 10 degrees warmer. While the infrared images are a snapshot in time, most of the cold pools are still there, in the exact same spot, Crandall said.
It's not uncommon for a cold-water pool to be 7 or 8 degrees Celsius, while just a short distance away, the river is 15 degrees – a crucial difference for fish, Crandall said.
These extra-cold pools provide an important refuge for fish when the main river starts to ice over.
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