A stream with two stories — but only because it goes dry in summer

Most people think of the Pacific Northwest as a region of dense coniferous rainforest and myriad gushing rivers that drain mountain ranges influenced by a damp, cool coastal climate. And it is. But like every other part of the American West, this region also features one of the most important components of any watershed: intermittent streams.

 

Small intermittent streams such as this one are much more productive than one would expect

Intermittent streams are those that flow only seasonally, or which may go dry in sections during the dry season or in periods of drought. In salmon and steelhead country, such streams play a very important role in the productivity of salmonid populations. In fact, intermittent streams do not just exist in the dry part of the Pacific Northwest east of the Cascades — they are more common and important to fish on the wet side of the Cascades than many people may think.

 

Unfortunately, a proposed action by the Trump administration could diminish or even eliminate protections for water quality in many of these critical streams. Given the importance of ephemeral and seasonal streams as habitat for steelhead, salmon and trout, this would be a significant setback in our efforts to recover these and other species of native coldwater fish.

 

I live on the west side of the Olympic Peninsula, which is the epicenter of the great Coastal Rainforest. Mt. Olympus, at almost 8,000’ in height, is the tallest peak in the Olympic Range.  The mountain, and its shorter cohorts, play a huge role in shaping the ecosystem. Any moisture that seeks to pass must pay a toll in precipitation. And there is no shortage of storms that seek passage. The sum collected by Mt. Olympus each year? An average of 220” of precipitation.

 

Despite its reputation as a “water world,” this is also a place of dry creekbeds in late summer.  Mt. Olympus can only force the clouds to rain, it cannot store the tolls it collects. By late July to early August, some of our creeks that were raging torrents over the winter go dry for long stretches.

 

It happens almost like clockwork every year. The same streams at the same time. How can such streams be so vital for steelhead and salmon? Let’s take a closer look at one such intermittent stream, which I’ll refer to as the “South Fork,” a medium-sized tributary in the Quillayute River watershed about 30 miles in length, for an answer.

 

 

Each summer, starting in July, the middle of the South Fork goes dry. The drying reach ranges from 7-12 miles long, depending on the year, though in some years streamflows in almost all of the lower 20 miles can go subsurface. This is amazing because flow in the South Fork can reach upwards of 2,000 – 4,000 cfs during winter high water episodes, so it is much more substantial than your average intermittent creek.

 

The South Fork supports populations of Chinook and coho salmon, steelhead, cutthroat, and mountain whitefish. It is both a critical spawning and rearing tributary for all these species, but more importantly, its ephemeral nature creates a situation that is very different from what is found in streams that never go dry — a situation that benefits both adult and juvenile fish.

Winter steelhead from a small Northwest stream

There are essentially two South Forks in summer: the wet and smaller sized stream above the drying reach and the lower and larger sized stream that goes dry below. By end of July the upper section is dominated by juvenile coho, steelhead and cutthroat trout. This area has the highest densities of rearing juvenile salmonids anywhere in the Quillayute watershed. It is a juvenile fish factory. In contrast, the lower section supports very few juveniles, but it does support a very robust population of cutthroat trout, some summer steelhead and a large number of mountain whitefish.

 

This habitat segregation seems to work for the fish. The juveniles in the upper reach are largely isolated from the bigger-sized cutthroat in the lower section, which reduces their chances of being eaten by them. The stream is also a bit warmer up high, in the 60-68°F range. The warmer water temperatures, in an otherwise cold place, help improve growth rates for juveniles and diversify the insect population that feeds them. It is an excellent nursery.

 

On the other hand, the lower reach is consistently much colder, with water temps rarely getting above 60°F and often hovering around 55°F. Why? Because the stream in this reach is fed by sub-surface flow that percolates to the surface after being chilled in the massive underground aquifer. That is good, because the adult cutthroat, steelhead, Chinook salmon and whitefish that use the lower reach rely heavily on those cold temperatures as thermal refugia during the warm and dry summers.

 

Once fall rains arrive and reconnect the two reaches of the South Fork, the segregated populations begin mixing again. The adults from the lower reach move up to spawn in the upper reach and the formerly dry section. The juveniles begin their migration downstream to use the floodplain and side channel habitat, and are now big enough that their chances of being eaten by hungry cutthroat are reduced.

 

And there the fish will remain through winter and spring, until the summer arrives again and the process starts all over. Adult steelhead and cutthroat that survived spawning will move downstream and back to the sea, leaving behind their juveniles to bask in the sanctuary of the upper reach.

 

Thousands of intermittent streams and their fish populations up and down the West Coast have similar stories, because salmon, steelhead and trout have evolved over millennia to take advantage of these unique habitats. In California, for example, almost 60 percent of stream miles that provide coastal steelhead habitat are classified as intermittent or ephemeral.

 

We won’t have clean water in our major steelhead and salmon rivers if we have polluted water in their sources. If we are serious about conserving these remarkable native fishes and the commercial and sport fisheries they support into the future, we cannot afford to degrade or destroy any more of their habitat. Join Wild Steelheaders United in telling the Trump administration to let well enough alone when it comes to Clean Water Act protections for critical wild steelhead habitat.

 

-John McMillan