How Stream Temperatures are Changing in the Valley

During the hot summer months, many of us take advantage of the Elk River to cool off, whether through swimming, wading or floating down the river. Although the river is still refreshing throughout the summer, we can all appreciate that it is warmer than during the freezing winter months. This begs the question: how do fish react to warmer water temperatures?

Water temperature can have a large impact on fish. When you think about it, it makes sense. We humans also struggle to accomplish basic tasks like cooking and chores when it’s very hot, right? Fish are similar, with each fish species having its own ideal temperature range. When water temperatures get too hot and rise out of this range, oxygen levels in the water can drop, which can impact fish development, metabolism (converting food to energy) and eventually cause fish death.

Westslope Cutthroat Trout, for example, have an ideal water temperature range of between 10 and 15°C. Once water temperatures rise above 20°C, the trout experience increasing stress, until temperatures become lethal to the fish around 25°C. Other fish species have different preferences, but most fish species found in the Elk River watershed, like bull trout or rainbow trout, have similar ranges and begin to experience stress at around 16 - 20°C. Those who fish, or who know someone who fishes, might notice that these temperatures also match the range around which we start to see fishing restrictions in BC.

Climate change throws another spanner in the mix, because as temperatures continue to change and hotter summers and more variable snowpacks become the norm, shifting stream temperatures become more of a concern for fish. This can especially be a concern in deforested watersheds, since shade from riparian forests can keep water 2-5°C cooler.

Over the past five years, ERA has been collecting temperature data from tributaries of the Elk River, throughout the valley. This data is collected to help paint the picture of how stream temperatures are shifting over time and to improve our understanding of which streams are nearing or exceeding the temperature tolerance levels of fish.

Looking at data collected so far, stream temperatures of Elk River tributaries are, on average, higher as you move further downstream in the watershed. The warmest tributaries measured are Coal Creek, Lizard Creek and Morrissey Creek, all of which regularly exceed 15°C, with lower Coal Creek and Morrissey Creek approaching 20°C during the middle of summer.

Temperature data is, by nature, quite variable. We have all seen how some years have long winter cold spells and others might have heat domes or summers marked by rainy cold periods. With 2-5 years of data collected for these Elk River tributaries, it is still too early to be able to say if we are seeing changes due to climate change. What we can already see, however, is which streams are the most likely to be the first to reach these critical temperatures that can cause fish to experience stress and potential death as climate change continues.

By understanding which streams are most at risk, we are much better able to inform decisions about when and where to fish, and how to help safeguard these fish species that are so important for both recreation and healthy stream ecosystems. At the same time, the Elk River Alliance will continue to collect temperature data to look at those more elusive, longer-term, climate change impacts.

This piece will be the last Water Column article in the Fernie Fix. For anyone interested in further writing, ERA will be continuing to provide content through our social media and our website!