Frequently Asked Questions
Twenty-Two Answers to Questions You May Have Had About Algae Blooms
When did the Gallatin River Task Force first become aware of an algae problem in the Upper Gallatin River Watershed?
The Task Force and the Montana Department of Environmental Quality (MT DEQ) first identified an “algae problem” in the West Fork Watershed in 2005 by monitoring both nutrients and algae biomass. Algae biomass data from 2005 and 2008 suggested that algae growth exceeded state standards in the West Fork and South Fork of the West Fork and was elevated in the Middle Fork of the West Fork.
In 2010, the West Fork Watershed TMDL study designated the West Fork, Middle Fork, and South Fork to be impaired or exceeding state standards for nutrients. This designation took into account algae biomass data.
The Task Force and citizens have documented a “green trail” from the West Fork confluence to the Big Sky Golden Gate bridge (about 3 miles downstream of the intersection of HWYs 191 and 64) for several years. The Task Force has documented algae growth at 21 monitoring sites with photos since 2014.
The Task Force received multiple reports of unprecedented algae growth on the mainstem Gallatin River in 2018. We are in the process of collecting algae biomass data for 21 sites on the Gallatin River, Taylor Fork, West Fork, Middle Fork, South Fork, and North Fork.
The Task Force and the Montana Department of Environmental Quality (MT DEQ) focused on monitoring algae in the West Fork Watershed between 2005 and 2017. The West Fork Watershed Total Maximum Daily Load study unearthed excess algae growth in the three tributaries in the Big Sky area: the West Fork, Middle Fork of the West Fork, and South Fork of the West Fork.
Citizens and Task Force staff have documented a “green trail” of algae beginning downstream of where the West Fork enters the Gallatin River and continuing to the Big Sky Golden Gate bridge (about 3 miles downstream of the intersection of HWYs 191 and 64), as well as an algae bloom below Wapiti Creek on the Taylor Fork, for several years.
In 2018, the Task Force received multiple reports of unprecedented algae growth in the mainstem Gallatin River downstream of the West Fork to Moose Creek, and from tributaries that flow into the Gallatin, including the South Fork of the West Fork, the West Fork, and the Taylor Fork. We have also received reports of spotty algae growth on the mainstem Gallatin River as far downstream as Storm Castle.
The Task Force is in the process of collecting and analyzing algae biomass samples from 21 sites located on the Gallatin River, Taylor Fork, West Fork, Middle Fork, South Fork, and North Fork to further investigate algae in the watershed. These analyses will help quantify the extent of algae growth, determine whether or not it is a threat to river health, and point to the cause of excess growth.
The Task Force received multiple reports in 2018 that algae growth in the Gallatin River was noticeably more prolific than previous years.
We have collected data that confirmed excess algae growth in the West Fork, Middle Fork of the West Fork, and South Fork of the West Fork over six different years (2005, 2008, 2013, 2014, 2016, and 2018). We have not been able to identify whether or not algae is becoming more widespread/prolific over time from these results; however, the inability to determine a long-term trend may be due in part to limited data, changes in Montana Department of Environmental Quality (MT DEQ) algae monitoring protocols, and the complex factors impacting algae growth.
In order to understand long-term trends, researchers must compare decades of data, rather than just a few years of measurements. To date, we do not have sufficient data to determine whether or not there are any long-term trends. In addition, the MT DEQ changed their algae monitoring protocol in 2006 making it difficult to compare data collected before and after that time. Finally, algae growth is affected by several factors that vary greatly year-to-year, including water temperature, sunlight, water clarity, nutrients, and streamflow.
Moving forward, the Task Force will continue to monitor the situation by conducting interviews with long-time river users about algae, continuing to take annual photos of algae at all of our field sites, and performing regular algae biomass assessments.
Does the Task Force anticipate these algae blooms will continue to occur every summer? Could they continue to get worse?
Although the Task Force cannot predict the conditions that may favor algae growth in the future, we have determined that both nutrient concentration and algae growth are currently elevated. If we have identified threats to water quality today, and we do nothing to address these impacts, algae blooms could continue or get worse as the Big Sky area grows and our global climate changes.
The Task Force and the Montana Department of Environmental Quality (MT DEQ) diagnosed three streams in the Big Sky area with elevated algae and nutrient levels: the West Fork, Middle Fork of the West Fork, and South Fork of the West Fork through a study that evaluated whether or not streams in the area met state water quality standards. Population growth could worsen the impacts to rivers and streams by increasing the need to treat and dispose of wastewater and expanding the impacts of residential and resort development to streamside and near stream areas.
In addition, the Montana Climate Assessment predicts the annual average daily temperature may warm by 5.6 to 9.8 degrees F across Montana by the end of the century due to anthropogenic climate change. This will warm water temperatures and extend the growing season for algae. Warming temperatures will also affect winter snowpack and midsummer water levels, which further enhances conditions conducive to algae growth.
According to email communication with the Montana Department of Environmental Quality (MT DEQ):
The MT DEQ has noticed significant changes in the timing and location of algae blooms on other western Montana rivers, most notably during 2016 and 2017. The MT DEQ is also more aware of algae blooms occurring during the past three to five years in many reservoirs in western Montana. Higher than average snowpack and spring runoff during 2018 provided a low to mid-range stream algae growth season within the region. The Gallatin River seems to be a regional anomaly of especially active growth and we are not sure why. The 2018 Gallatin algae conditions are on MT DEQ’s emerging topics list and the MT DEQ is coordinating with the Gallatin River Task Force and others to a keep pulse on the situation. MT DEQ will coordinate with the Task Force to compile and analyze data this winter.
Excess nutrients, warmer temperatures, or other factors can cause algae blooms, which may have a negative impact on fish and their food sources.
At first, algae blooms alter aquatic insect habitat, which may increase the rate of some insect hatches while decreasing others. In addition, algae blooms are unsightly and can be a nuisance when swimming or fishing.
Finally, severe algae blooms can lead to additional plant biomass in the ecosystem that must be broken down by microorganisms. When bacteria decompose the extra plant matter, they consume oxygen dissolved in water that fish and aquatic insects need to survive.
Algae begin to grow in the spring when the days lengthen and the water warms and die in the fall. The Montana Department of Environmental Quality (MT DEQ) defines the algae growing season to occur between July 15th and September 30th. During the average year, algae grow and die within this window.
Algae blooms are not triggered by a single factor, but rather, variation in some combination of the following conditions:
- Nutrients: Nutrients, like nitrogen and phosphorus, fuel algae growth; however, excess nutrients from human activities can trigger or exacerbate algae blooms.
- Temperature: Generally speaking, warmer water leads to increased algae growth. The temperature of the water may even favor the growth of certain types of algae over others.
- Streamflow: Algae prefer stable conditions. Low water levels create slower, more uniform conditions that encourage algae growth.
- Consecutive years of low spring runoff: High or prolonged spring runoff can scour algae basal cells off of rocks and set the growing season back. Multiple years of low runoff can produce early algae blooms.
- Light: Like land plants, algae need sunlight to grow. Sunny reaches tend to have more algae growing in them than shaded reaches.
- Turbidity (water clarity): Particles suspended in streams affect how light travels through the water. More sunlight penetrates clear water contributing to algae blooms.
- Size of rocks on the stream bottom: Long stringy algae (usually Cladophora) prefer stable cobble stream bottoms because they don’t shift during low flow and are typical of riffle areas that have preferable water velocities.
For more information, visit the Center for Earth and Environmental Science at Indiana University website.
We can impact algae growth in the following ways:
- Nutrients: Nitrogen and phosphorous are two essential nutrients for plants and animals that can cause a cascade of negative effects in river ecosystems. The main sources of nitrogen identified by the EPA are agriculture through manure and fertilizer; stormwater, which carries pollution to rivers; wastewater, including treated effluent and septic systems; household sources like fertilizer, pet waste, etc.; and fossil fuels.
- Temperature: The Montana Climate Assessment predicts the annual average daily temperature may increase by 5.6 to 9.8 degrees F by the end of the century. This will warm local rivers and streams exacerbating algae blooms.
- Streamflow: Warmer temperatures may affect water supply by causing more precipitation to fall as rain, rather than snow. This could decrease winter snowpack, which feeds waterways throughout the hot, dry summer. Furthermore, our public water supply comes from groundwater, which is highly connected to rivers and streams in our area. As the Big Sky community grows, increased water use will threaten water levels in rivers and streams. Low water levels contribute to warm, stable conditions conducive to algae growth.
- Light: Streamside plants, like willows, shade waterways. Removing streamside plants during development may encourage algae growth by increasing the amount of light that reaches streams and warming streamwater.
- Stormwater: Removing vegetation and disturbing the ground during residential and resort development loosens and exposes soil, which is full of nutrients. Then, wind and water carry soil and nutrients downhill to rivers and streams. In addition, the particles suspended in cloudy water absorb more heat.
Learn what you can do to protect local rivers and streams here.
Individuals can take action to help reduce nutrient pollution and algae blooms! Here are a few simple ways that you can be proactive:
- Maintain or restore streamside vegetation on your property
- Use Trout Friendly practices when you landscape, like applying the proper amount of fertilizer
- Pick up and properly dispose of pet waste
- Select phosphate-free detergents, soaps, and household cleaners
- Ensure that your septic system is functioning properly
- Move animal feedlots and corrals away from streams
- Use stormwater best management practices during construction
- Advocate for science-based management decisions that protect rivers and streams in your community
The Task Force and volunteers monitor nitrate levels four times a year through our Community Water Quality Monitoring Program. In addition, we monitor total nitrogen and total phosphorus once a year during the growing season sampling event.
Our program includes 21 sites in the Upper Gallatin River Watershed. These sites capture the influence that geology and land use may have on our river system. We monitor all our sites quarterly to track changes in water quality across hydrological regimes, such as high flow versus low flow, and biological regimes, such as the growing season versus the dormant season.
For more information on our monitoring program, read our Sampling Analysis Plan here.
Does Gallatin River Task Force use an instrument that allows nitrate levels to be measured in the field?
No. To our knowledge, instruments that measure nitrate in the field do not have the resolution necessary to measure nitrate in low-nutrient streams, like the Gallatin River and its tributaries.
The Task Force fills bottles with stream water from our 21 field sites. Then, we analyze these samples in a laboratory. Our staff adds chemicals to the water to cause a reaction, which turns the sample pink if there is nitrate present. The shade of pink varies with the concentration of nitrate in the sample.
After the reaction is complete, we analyze these samples using an instrument called a spectrophotometer. This instrument passes light through the sample to detect the intensity of the pink color and to quantify the amount of nitrate in the sample.
During our summer baseflow event, we collect our samples and send them to Energy Laboratories to be analyzed for nitrate, total nitrogen, and total phosphorus. Nutrient levels during the growing season have the biggest effect on river health, so we want to make sure data from our summer events are as accurate as possible.
The Montana Department of Environmental Quality (MT DEQ) funds our summer nutrient analyses through a program that supports volunteer water quality monitoring.
In 2018, the Task Force measured among the highest summer nitrogen levels in the West Fork upstream of the South Fork confluence: 0.42 mg/L for total nitrogen and 0.31 mg/L for nitrate. In contrast, the state standard for total nitrogen is 0.3 mg/L. The state standard for nitrate was removed by the Montana Department of Environmental Quality in 2013; however, the Task Force still uses the previous standard of 0.1 mg/L as a trigger value for elevated nitrate in local streams. The only historical nitrate measurements similar to the summer 2018 values were collected at two sites on the West Fork downstream of the Big Sky Community Park in August 2008.
Average nitrate levels from 2000 to 2016 were between 0.01 mg/L and 0.07 mg/L on the mainstem Gallatin and between 0.02 mg/L and 0.18 mg/L in the West Fork Watershed. The average nitrate levels exceeded the recommended level (0.1 mg/L) at the two West Fork sites (“Community Park” and “West Fork above South Fork”) downstream of the golf course and upstream of the South Fork confluence.
Average total phosphorous levels (summer only) ranged from 0.0048 mg/L to 0.022 mg/L on the Gallatin River and between 0.0063 mg/L to 0.013 mg/L in the West Fork Watershed. On average, all sites were below 0.03 mg/L critical value used by the Montana Department of Environmental Quality (MT DEQ).
Average total nitrogen levels (summer only) fell between 0.08 mg/L and 0.10 mg/L on the Gallatin River and between 0.09 mg/L and 0.25 mg/L in the West Fork Watershed. On average, all sites were below the 0.3 mg/L critical value used by the Montana Department of Environmental Quality (MT DEQ).
For more information, check out this review of our community water quality monitoring data from 2016.
Plants convert nutrients, including nitrogen and phosphorous, into biomass. Nutrient uptake is just one factor that contributes to changes in nutrient levels throughout the year.
We have observed a strong seasonal cycle in nitrate concentrations in the Upper Gallatin River Watershed by monitoring nitrate quarterly. Nitrate is a form of the nutrient nitrogen that is readily available to plants and animals.
Nitrate levels are highest in the winter. During the cold, dark winter months, dormant algae and aquatic plants use less or minimal nitrate in stream water. In addition, low water levels further concentrate nitrate levels.
During high water in the spring, the concentration of nitrate decreases when snowmelt feeds rivers and streams. Nitrate levels continue to diminish during the summer growing season when algae use nutrients to grow. To account for algae consumption of nutrients, we collect both nutrient and algae biomass data during the summer. Nutrient levels begin to increase again in the fall as algae die and water levels drop.
The seasonal nitrate cycle is similar in the streams in the Big Sky area; however, the magnitude of the winter nitrate peak is consistently much higher in the West Fork than any other stream in the area due to human sources of nitrogen in the Big Sky area.
The Task Force published a review of our community water quality monitoring data in 2016. The report identified strong spatial and seasonal trends in nitrate levels, but no conclusive long-term trends.
Nitrate is a form of nitrogen readily available to plants and animals. If nitrate exceeds 0.1 mg/L during the growing season, elevated nitrate may accelerate algae growth, which impacts recreation and aquatic insect habitat.
Average nitrate levels from 2000 to 2016 were between 0.01 mg/L and 0.07 mg/ on the mainstem Gallatin and between 0.02 mg/L and 0.18 mg/L in the West Fork Watershed. The average nitrate levels exceeded recommended levels (0.1 mg/L) at the two West Fork sites (“Community Park” and “West Fork above South Fork”) downstream of the golf course and upstream of the South Fork confluence.
Across the watershed, nitrate was highest in the fall and winter when water levels were low. Sixteen years of nitrate data demonstrated no conclusive long-term trends. This may be due in part to limited data and the variety of factors influencing nitrate levels, including streamflow and human influence. Our results from 2017 supported the trends observed between 2000 and 2016.
In 2018, the Task Force measured among the highest summer nitrogen levels in the West Fork downstream of the golf course and upstream of the South Fork confluence: 0.42 mg/L for total nitrogen and 0.31 mg/L for nitrate. In contrast, the state standard for total nitrogen is 0.3 mg/L. The state standard for nitrate was removed by the Montana Department of Environmental Quality in 2013; however, the Task Force still uses the previous standard of 0.1 mg/L as a trigger value for elevated nitrate in local streams. The only historical nitrate measurements similar to the summer 2018 values were collected at two sites on the West Fork downstream of the Big Sky Community Park in August 2008.
Yes, all Task Force data, publications, and reports are available on our website:
Would an upgrade to the Big Sky Water and Sewer District treatment plant help to lessen these algae blooms?
If an upgrade to the Big Sky Water and Sewer District treatment plant resulted in treated wastewater with a lower nutrient content, this could lessen nutrient loading to local rivers and streams via wastewater irrigation. Lower nutrient levels in recycled water used to irrigate the Big Sky Resort golf course could decrease one source of nutrients to the West Fork and reduce the prevalence and extent of algae blooms. Due to the complex nature of nutrient transport to rivers and the many factors driving algae blooms, we cannot predict how treatment plant upgrades would impact algae growth with any certainty.
At this time, the Task Force is working hard to understand the impacts of the 2018 algae bloom. We are concerned about the unprecedented level of algae growth in 2018. If nuisance algae growth continues or worsens, it could have serious implications for the health of our river.
We will not be able to determine the scope and implications of the 2018 algae bloom until we have acquired and thoroughly analyzed our monitoring data. By evaluating nutrient levels, algae biomass data, and other indicators of river health with experts from the Montana Department of Environmental Quality (MT DEQ), we will understand more about the underlying factors that caused excess algae growth.
A group of citizen scientists started collecting routine water quality data in 2000 to build a baseline understanding of river health in the Upper Gallatin Watershed.
Then, the Montana Department of Environmental Quality (MT DEQ) conducted an intensive study between 2005 and 2010 to identify threats to water quality in the Big Sky area. This study, known as a Total Maximum Daily Load (TMDL) study, evaluated whether streams in the area were healthy enough to meet state water quality standards for recreation, fisheries, public water supply, and other beneficial uses.
Data from 2005 and 2008 suggested that algae growth exceeded state standards on the West Fork and South Fork of the West Fork and was elevated on the Middle Fork of the West Fork. In 2010, the West Fork Watershed TMDL study designated the West Fork, Middle Fork, and South Fork to be impaired or exceeding state standards for nutrients.
Check out these resources with more information on algae and water quality in the Upper Gallatin River Watershed:
Gallatin River Task Force Community Water Quality Monitoring Program:
- Community Water Quality Monitoring Program Data
- Community Water Quality Monitoring Program Sampling Analysis Plan
- 2016 Upper Gallatin River Watershed Water Quality Report
- 2017 Upper Gallatin River Watershed Water Quality Report
West Fork Gallatin River Total Maximum Daily Load Study:
- Upper Gallatin River Watershed Impaired Streams
- 2005 Biological Monitoring – Chlorophyll-A
- 2008 Water Quality Monitoring Report
- 2010 The West Fork Gallatin River Total Maximum Daily Loads (TMDLs) and Framework Watershed Water Quality Improvement Plan
West Fork Nitrogen Study and Watershed Restoration Plan
Could algae growth in 2018 have been caused by the wastewater treatment pond leak at the Yellowstone Club?
Excess algae growth in 2018 is unrelated to the wastewater treatment pond leak that occurred at the Yellowstone Club in early March 2016. The treated wastewater spill increased levels of nitrate and ammonia in Second Yellow Mule, South Fork, and West Fork in the days immediately following the spill; however, there were no long-term effects to water quality.
The largest impact to river health after the spill was caused by excess fine sediment carried from the steep hillside beneath the wastewater treatment pond to Second Yellow Mule and the South Fork. Excess fine sediment can cause a cascade of negative impacts to fish and stream insects by covering spawning habitat, clouding water, and impacting their gills. Montana Fish, Wildlife, and Parks reported that fish and stream insect population would recover in Second Yellow Mule Creek and the South Fork in several years.
For more information, the Gallatin Task Force developed a webpage with more information on the incident: https://www.gallatinrivertaskforce.org/yellowstoneclubspill/.