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.
Crandall’s initial goal is to identify and map all the cold-water patches, so people are aware of them and can take steps to ensure they don’t become degraded. The cold water occurs on private, state and federal land. Ultimately, Crandall would like to see projects that enhance the cold areas to provide more benefits to fish.
There are various strategies for protecting these cold springs and pools. Placing a log structure in the river could make the cold water deeper and isolate it so it doesn’t get diluted by warmer parts of the river. That would also create a protected space for fish to hide, Crandall said.
Another approach would be for the county to flag these cold-water patches on building permits and site plans. “It’s a logical step in land-use planning,” Crandall said. “It’s a respectful thing to do for the land.”
He’d also like to see cold-water refugia accorded formal protection by the state regulations that protect other critical areas.
Finding the cold spots
Most of us go about our days oblivious to these extra-cold spots. One of the most reliable sources of cold water is easily visible from the Tawlks-Foster Suspension Bridge in Mazama, a popular year-round destination on the trail system.
From the bridge, looking upstream toward Mazama, it’s easy to spot Suspension Creek on the left, a small tributary that flows into the Methow River.
In late summer and fall, the mainstem of the upper Methow River is so low that parts of it look like dry cobbles. But there’s still water flowing below the rocks. When the water level comes back up, it can mix with the cold groundwater from Suspension Creek, Crandall said.
Good water quality is also important to humans for drinking, irrigation, and cooling off in the summer. Warming affects the pH of water, which in turn affects the crops watered with it.
Threats to cold water
Scientists have been keeping detailed, consistent year-round records of water temperature in the Methow for only about a decade.
Many things threaten cold water, including development, the clearing of riparian vegetation, and the effects of climate change, Crandall said. Not surprisingly, hot weather warms the water and, when river levels are low, the water warms even faster. Shade can protect it from warming further, but it won’t actually cool it off.
Other sources of warming are increased sediment in rivers and streams and the loss of floodplains. Wildfires can affect water temperature by reducing shade and increasing sediment, Crandall said.
Although models of the changing climate project significant warming by 2040, some streams have already reached those temperatures, Crandall said.
The Chewuch is warmer than the Methow because its headwaters are at a lower elevation. The Twisp River is especially cold, making it key habitat for bull trout.
All three rivers are already warmer than they should be, and they don’t meet the state’s water-quality criteria for native fish, Crandall said. Data he’s collected from 2013 to 2019 shows that temperature impairment in the Methow watershed is already widespread.
Vital for fish
Cold water is a matter of life and death for already endangered salmonids and bull trout in the Methow Valley. Fish are ectotherms, meaning they’re at the mercy of water temperature.
Water temperature and volume determine when fish hatch, migrate, swim to the ocean and spawn. When water is too warm, the fish’s metabolism increases, so they burn more calories and need to eat more. It affects reproduction and makes them more susceptible to disease, Crandall said.
Spring Chinook are especially vulnerable, because they spawn during the warmest part of the year and have to search for cold water to lay their eggs. Because steelhead spawn in the spring when the water is really cold, they have more flexibility.
Although some fish are less productive when the water is too warm, bull trout can’t survive without cold water, Crandall said.
Water temperature is also crucial for when fish eggs hatch, since they need a certain number of days with water temperature above freezing. As the climate warms, eggs may hatch early, but the aquatic insects the juveniles eat might not be on the same schedule. “Fish can’t just eat moss – bugs are the cheeseburgers,” Crandall said.
Providing the best possible habitat is crucial to help fish that already face multiple obstacles to survival. Young fish also need floodplains at the right time of year as refuge.
On their return from the ocean, in some years, up to one-quarter of the adult spring Chinook are eaten by sea lions before they reach Bonneville Dam on the Columbia River Gorge. In some years, 20 to 50% of the spring Chinook that pass through Wells Dam, south of Pateros, die before they can spawn – and those are the survivors, Crandall said.
As a result, on average, only a few hundred spring Chinook make it back to the Methow to spawn. That’s why enhancing the cold water here could have a significant impact on their survival, he said.
The cold-water mapping project is funded by a $40,000 grant from the Public Utility District Tributary Fund of the Douglas and Chelan county PUDs. The primary project partners are the Methow Salmon Recovery Foundation and the Bonneville Environmental Foundation.