Marathon Runners of the Rogue

Imagine running a marathon while the air around you is filled with smoke. You’d get tired quicker, have uncontrollable coughing, and eventually, give up entirely. You may not think oxygen is as important to fish as it is to humans, but this analogy is perfect for our salmon and coldwater fish populations. Fish actually breathe the air (oxygen) inside the water. Remember, water is H2O– and that O means something! It is the key to determining if a migrating salmon is a champion athlete or floundering at the starting line.

The amount of what we call “dissolved oxygen” in the water is critically important for fish. Dissolved oxygen is the amount of gaseous oxygen dissolved in water, and aquatic organisms need it to survive. So how does it get there? 

ROCKS! There’s a reason we often put large boulders in our projects. As water tumbles and churns over and around rocks (and waterfalls), it grabs oxygen from the air.

Check out this oxygenating action at West Fork Trail Creek River Mile 1.5

PLANTS! The slimy but beautiful plants underwater “exhale” oxygen during the day through photosynthesis. Although plants are important to aquatic communities, we also don’t want to see them take over (think algae covering an entire lake). It might help oxygen levels in the short term, but dense mats also absorb more sunlight and increase water temperature… but that’s a topic for another time.

ATMOSPHERE! Some of the dissolved oxygen comes directly from the atmosphere through diffusion (and even wind).

Looping back around to temperature, there’s a unique connection between dissolved oxygen and water temperature. Cold water holds more oxygen than warm water– similar to how a can of cold soda holds more bubbles than a warm, flat one. This is one of the reasons why we see more fish kills in the summer– rising water temperatures lead to lower oxygen levels, and that results in large die-offs of aquatic life.

Guess what else uses dissolved oxygen? Bugs! Aquatic macroinvertebrates need dissolved oxygen to survive, and some species are particularly picky when it comes to these levels. Those protein-packed crawlers are a key piece of many fish diets, including salmon.

We’ll be watching closely to see how our winter of low snowpack and drought impacts water temperature and dissolved oxygen levels across the basin. Our work this summer, as always, will increase the resilience of Rogue River Watersheds. Shaded stream channels stay cooler longer, increasing dissolved oxygen levels. Healthy riparian areas and connected floodplains feed cold groundwater into streams, even in the summer. Removing barriers (like the culvert removal projects we have slated for this summer) and replacing them with carefully installed rocks and logs increases oxygen uptake. As salmon run their marathon from the Pacific Ocean towards the headwaters of the Rogue, high dissolved oxygen levels help them make it to the finish line.

*Fun fact, the levels of dissolved oxygen also affect how your drinking water tastes. Generally, the higher the level, the better the taste. As always, rivers that are healthy for aquatic life are better for humans. So the next time you think about how exhausting a marathon is, take a minute to think about how taxing the journey would be with low oxygen!