Clearwater Lakes Alliance Information
Disclaimer: For a general intro to lake ecology and a list of terms used below, check out the CLA home page.
~ Big Sky Lake ~
Big Sky Lake, Photo by J. Harrits
Lake monitoring on Big Sky Lake. Photo by C. Harrits
About Big Sky Lake
Figure 1: Location of Big Sky Lake within the Clearwater Watershed
Big Sky Lake is located about 1 mile northeast of Salmon Lake (Figure 1). Access to Big Sky Lake for fishing and recreation is limited to property owners and their guests. This privatization has allowed Big Sky Lake to remain relatively pristine in nature. At about 94 acres in surface area and 55 feet in depth, Big Sky Lake is one of the smallest and shallowest monitored lakes in the Clearwater Basin.
Past Monitoring
The temperature and water clarity of Big Sky Lake have been monitored through our Adopt-a-Lake program since 2009 (Figure 2). Big Sky Lake has some of the deepest recorded Secchi depths of the lakes in the watershed, typically ranging from about 15 to 25 feet, placing it well within the oligotrophic depth boundary (Figure 3).
Figure 2: Secchi depths recorded at Big Sky Lake from 2009 through 2020.
Figure 3: Secchi depths recorded at 15 sites on 8 lakes in the Clearwater Watershed, 2009 through 2020. The red and green lines represent the bounds for transparencies considered indicative of eutrophic and oligotrophic conditions, respectively. Note that as of 2020, Clearwater and Rainy Lakes were omitted from monitoring.
Dissolved oxygen (DO) levels were not previously monitored in Big Sky Lake until 2020. The first DO reading was taken on May 21, 2020. In 2020, CRC undertook DO monitoring on Big Sky Lake to give us a better idea of current conditions and whether water quality is declining. In addition to Big Sky Lake, DO profiles were taken on 5 other lakes in our watershed (Salmon, Seeley, Placid, Alva, and Inez) on a monthly basis throughout 2020 to establish a baseline DO dataset.
Figure 4: Dissolved oxygen (mg/L) profile recorded at one site in Big Sky Lake, from July through September 2020.
Figure 5: Temperature (°C) profile recorded at one site in Big Sky Lake, from July through September 2020.
Big Sky Lake surface DO levels were at their greatest in July, but lower in August and September (Figure 4). The July DO profile taken on Big Sky Lake was the highest of any of the readings taken in 2020, peaking at 13.42 mg/L at 5 meters in depth. Although nothing visually anomalous was noted in the water on that monitoring day (7/30/20), it is possible that this reading indicates the growth of a near-surface algae bloom, which would increase DO in the epilimnion through photosynthetic activity. The hypothesis of an algae growth is supported by the Secchi readings, which exhibited a marked decrease in transparency around the time this DO reading was taken (Figure 2). This specific decrease in transparency was unique to Big Sky Lake, as most of the other lakes were exhibiting maximums or slight fluctuations in transparencies at this time.
Current and Future Monitoring
Figure 6: Dissolved oxygen monitoring on Big Sky Lake.
Photo by J. Harrits
Water Quality
Drawing conclusions based upon the sporadic data that currently exists is difficult, and more consistent measurements are needed to better assess the status of each lake in the valley. In 2021, CRC is collecting data on DO, conductivity, algae, nutrient, and pH conditions on Big Sky Lake (as well as Alva, Inez, Placid, Salmon, and Seeley) in order to continue establishing baseline data to aid in future water quality analyses. We will be analyzing this data to evaluate the health of our aquatic ecosystems in the Valley. This includes looking for trends in Nitrogen and Phosphorous levels, presence of E. coli bacteria, evidence of oxygen depletion, growth of potentially toxic algae, and other changes to the waterbodies in the Clearwater Watershed.
Figure 7: Water quality monitoring site on Big Sky Lake.
A new addition to the monitoring process this year is a multiparameter water quality monitoring instrument. This new piece of equipment was recently purchased thanks to a Bureau of Reclamation WaterSMART grant. It uses sensors to accurately read and record levels of conductivity, algae, and pH as deep as 30 meters (~100 feet) in our lakes. Such data is integral to determining the health of our lakes here in the Clearwater Watershed and can aid in detecting harmful algal blooms and habitat degradation.
Check back in the fall or winter for results and findings from our monitoring season!
Aquatic Invasive Species (AIS): Zebra and Quagga Mussels
Figure 8: 11 lakes in the Swan, Clearwater, and Blackfoot drainage basins were monitored for AIS in 2020. In order, as labeled, these lakes include: Holland, Lindbergh, Alva, Inez, Seeley, Placid, Big Sky, Salmon, Upsata, Coopers, and Browns.
CRC has been monitoring for invasive species in the Clearwater Watershed throughout the summers since 2009 on each of the major lakes in the Valley (Alva, Inez, Seeley, Salmon, Placid and Big Sky). One of the biggest threats to Montana’s waterways is the introduction of zebra and quagga mussels, collectively referred to as dreissenid mussels. The purpose of our AIS program is to monitor for the presence of veligers in the lakes by straining large volumes of lake water through a fine mesh net to collect planktonic and microscopic materials in the lake water, including mussel veligers, if present. Veligers are the free-swimming, microscopic juveniles of zebra and quagga mussels. Over the course of the 2020 field season, 62 total sites, spread out over 11 lakes (Figure 8), were sampled each round, totaling 310 samples.
We are happy to report that zebra and quagga mussel veligers were undetected in all of the samples collected and analyzed in 2020. We will continue to monitor for zebra and quagga mussel veligers throughout 2021 on the six major lakes in the Valley.
Through CLA, we hope to involve more residents in our citizen science Adopt-a-Lake program to expand the parameters we monitor and increase our monitoring frequency. CLA will also help us to take steps to actively improve the water quality of the lakes, which over time will hopefully be evident through the monitoring data we collect.
Establishing baseline monitoring data through our Adopt-a-Lake program is only the start. Contact CRC’s Dave Torell, (email: dave.torell@crcmt.org ) to learn more about current efforts and/or how you can get involved.
Return to the Clearwater Lakes Alliance main page.
Last updated September 2021