Seeley Lake, Montana – The Clearwater Resource Council (CRC) recently released a report on the findings of its water quality monitoring over the past two years. CRC collected water samples from six lakes in the Clearwater Valley in 2021 and 2022: Lake Alva, Lake Inez, Placid Lake, Salmon Lake, Seeley Lake and Big Sky Lake.
The community of Seeley Lake has no central sewage system, relying on individual septic systems. This has led to concerns that groundwater may be contaminated from poorly functioning or concentrated densities of septic systems, which may then leach to surface waters. The Seeley Lake Sewer Board has recently expanded its groundwater sampling program around Seeley Lake to determine if a problem exists. CRC is coordinating with this program to sample surface waters, not only in Seeley Lake but in five other lakes in the Clearwater Valley as well. The community obtains its drinking water from Seeley Lake, so any contamination of the surface waters would not only have significant impacts to the environment and recreational activities but could directly risk the health of the community.
Lakes typically stratify into different temperature zones over the summer, with the epilimnion being the upper, warmer zone, the metalimnion containing the thermocline where a marked change in temperatures occurs, and the hypolimnion deeper in a lake where cooler waters persist. The epilimnion is influenced by wind action as well as having available sunlight that triggers photosynthesis, both of which add oxygen to the water. Dead plants or other organisms typically sink to the hypolimnion where decay by bacteria occurs which uses up oxygen in the water.
The report includes data on various water quality parameters, but of particular interest are the results pertaining to the status of selected nutrients in the lakes. The findings generally supported that most of the lake parameters are consistent with natural lakes for this area.
Dissolved oxygen (DO) readings decreased in deeper waters of all lakes as the summer progressed, with all lakes dropping below 5 mg/L in the hypolimnion by fall. Dissolved oxygen commonly decreases with depth in lakes, so this finding is not unusual. DO levels in deeper areas of lakes recovered when the waters of the lakes turned over with changing temperature profiles in the fall. However, Big Sky Lake was found to have low DO levels in its deeper areas throughout the year. The cause of this low dissolved oxygen is not clear from the last two years of sampling. However, results of the nutrient sampling may point to a complicating cause.
Nutrient sampling of the six Clearwater watershed lakes generally found normal levels (100-200 ug/L) of total nitrogen and phosphorous for natural lakes. Higher levels of nutrients were found in deeper samples than in surface samples. Big Sky Lake is of particular concern. In 2022 nitrogen levels in two samples of surface water were 374 ug/L and 402 ug/L, while deep samples recorded 1700 ug/L and 1860 ug/L. There are no established nutrient standards for lakes in Montana, but these concentrations can be considered high, and their causes may need further research.
An interesting finding for Seeley Lake was in samples collected at the outlet of the lake, where consistently higher levels of nitrogen and phosphorous were found. This outlet is at the end of the relatively shallow and narrow still water section of the Clearwater River. Causes for this increase are unknown, but the shallow waters slowly flowing through this area where it passes by the presence of a number of cabins along the shoreline could be a factor.
The presence of harmful algal blooms (HAB) and other algae was tested by looking at the reflectance of algae (how much light they reflect). Estimates of total algal production and estimates of cyanobacteria (blue green algae) were made using a fluorescence technique that measured the presence of chlorophyll. Waters with high levels of chlorophyll indicate that such lakes are typically high in nutrients, specifically phosphorus and nitrogen that support the growth of algae. Sampling results for chlorophyll and blue-green algae were all found to be in relatively low levels, except for Big Sky Lake. Big Sky Lake exhibited levels of chlorophyll and phycocyanin (a pigment in algae) that were sometimes twice as high as those measured for the other lakes.
Algal blooms have not been reported in Big Sky Lake but have been noted in several of the other lakes in recent years. Additional sampling is needed to better understand the risk of HAB occurring on the Clearwater lakes.
Because the sampling of nutrients across the six lakes was quite limited for some lakes and varied across sampling dates, more sampling of nutrients is needed to establish a thorough baseline for water quality conditions. Additional nutrient sampling is being conducted in 2023 and should provide additional insights into nutrient concentrations in the lakes.
The results of the sampling are included in the project report that can be found on CRC’s webpage (www.crcmt.org). Results have also been shared with the Seeley Lake Sewer Board, Missoula County Health Department, Montana Department of Natural Resources and Conservation, and Montana Department of Environmental Quality. The project was funded through a grant from the Missoula Conservation District using monies provided by the Montana Department of Natural Resources and Conservation along with a grant from Monitoring Montana’s Waters and the assistance of volunteers.
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