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Every Drop Counts: Seasonality of the Gallatin River  

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Each of the four seasons represent an important time for the health of rivers like the Gallatin. COURTESY OF JESS OLSON


Live in Big Sky long enough and you’ll likely spend some time on the Gallatin. And with time, comes observation. How the weather affects the river from season to season is sometimes easy to see, and sometimes not. Either way, we are always aware when the color changes, or algae shows up, or the river is running at higher or lower flows.  

Seasonal patterns have a lot to do with the changing and evolving health and condition of a river, from its mainstem through to its tributaries; from water color to varying flows, to how the fish habitat presents itself, and what kind of algae growth (or how much, and where) we might or might not see.   

Varying levels of drought are also always a good factor to focus on. Because Big Sky experienced such a wet summer in 2023, the concerns for drought today are less relevant than other years, but still worth acknowledging. Referencing past years’ rainfall, moisture, snowfall, runoff, and other variable components of a river’s reactive health show us just how unpredictable the river can be. Backed with over 20 years of data, the Gallatin River still surprises us. This is why rigorous, long-term studies are important to understanding the natural world. Based on science and our own knowledge of the seasonality of the Gallatin River, here are a few thoughts worth sharing on each season:  


Spring presents snowmelt and consistent potential for rainfall, contributing to the highest water levels of the year. As the weather warms, snow starts melting from the peaks. At lower elevations, snow turns to rain, which creates the perfect storm for the river to reach its highest levels in the spring and early summer.  

During these times—and during other rainfall events year-round—the river often appears cloudier as more water moves through the system at a much faster pace. Sediment from river banks and runoff from snowmelt ‘dirty up’ the water, making it look brown or gray. While it may not be the Gallatin’s most attractive time of year, cloudy water is normal for spring, and something we expect year after year. Ideally, we like to see slower snowmelt throughout the spring and early summer to help replenish the aquifer and keep streamflows consistent. 


Summer snowmelt brings about our primary aquifer recharge. In the arid West, we do not typically experience high volume rain during the summer, and rely on the consistent, slower snowmelt to keep our rivers high and cool throughout the season. From what we understand so far, summers that deliver lower flows and higher temperatures can also bring about the perfect environment for algae to bloom and thrive.  

This past summer, Big Sky experienced much more rainfall than usual which kept our streamflows relatively high compared to past years in which we experienced typical drought conditions. From several summers of studying these blooms, we believe that higher rainfall, lower temperatures, and other changes to summer conditions likely prevented the recurrent algal bloom that led the Gallatin River to be designated as impaired for nuisance algae. This supports the scientific-backed information that leads us to know that there are several factors that contribute to these situations in a river’s health.  

Large amounts of rainfall can also cause more sediment to flow through the river at higher volumes, like we typically see in the spring. Often, this sediment is loaded with excess nutrients that can contribute to algal blooms. In recent summers, we experienced large, widespread algae blooms even after significant rainfall, and suspect that the influx of nutrients promoted algae growth. Though Big Sky did have several large rainfall events this year, we did not see the same response.  


It is a fact that what appears as rain at lower elevations like in the meadow, exists in colder temperatures as snow up on the top of Lone Mountain. Early fall can still feel like summer, but elevation is nine-tenths of what happens to precipitation. Fall brings lower flows to the Gallatin. With sporadic rain and early snow events, and even with warm temps, monitoring the Gallatin for algae in September and early October is a priority for the Gallatin River Task Force. These tactics help establish and record baselines, and understand any consistencies in river health that are worth noting over time, recording seasonal data.   

The Gallatin River in fall. COURTESY OF JESS OLSON


Snowpack, snowpack, snowpack. With lower winter flows, what we hope for is enough snowpack to help us repeat the healthy cycles of spring, summer, fall in the coming year. While we can never predict what the spring and summer will bring, we always hope for more snow. What’s good for skiing is even better for the river.  

Changing climate patterns indicate that we will see longer and more extreme droughts, and snowpack is our number one defense to help us through these periods. For the health of the river, and so many additional reasons, we prioritize broad water conservation practices as important pieces of our water resilience puzzle; not just in times of drought, but year-round.  

Jess Olson is the conservation manager for the Gallatin River Task Force.  

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