Seth A. Siefken Chad B. Reese 20250313 comma-separated values (CSV) Reston, Virginia U.S. Geological Survey https://doi.org/10.5066/P143QAKP This data release contains water quality data from discrete sonde profiles taken at 10 sites on Lake Koocanusa from 2019 through 2024. The profiles include measurements of water temperature, specific conductance, dissolved oxygen, pH, turbidity, and chlorophyll relative fluorescence as well as the depth of the sonde below the water surface. These data were collected as part of a water-quality monitoring program in Lake Koocanusa to provide data for Federal, State, Provincial, and Tribal entities in the United States and Canada. The data were collected to support monitoring of transboundary water quality in Lake Koocanusa and the Kootenai River. 20191003 20241211 observed Complete None planned -115.3083 -115.1650 49.2290 48.4141 Spatial domain consists of ten monitoring sites in Lake Koocanusa. ISO 19115 Topic Category environment inlandWaters USGS Thesaurus surface water quality water quality water temperature water pH turbidity oxygen content (water) water properties water chemistry USGS Metadata Identifier USGS:67746f54d34eea454343c695 Common geographic areas North America Canada United States Kootenai Lake Koocanusa British Columbia Montana None. Please see 'Distribution Info' for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Seth Siefken U.S. Geological Survey Wyoming-Montana Water Science Center Hydrologist mailing and physical

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Helena MT 59601 USA 406-475-4626 ssiefken@usgs.gov https://www.sciencebase.gov/catalog/file/get/67746f54d34eea454343c695?name=LakeKoocanusa_2024_06_12.jpg Molly Moloney, Jonathan O'Connell, and Madison Goodman collecting water samples and vertical sonde profile at Lake Koocanusa. Photo by Seth Siefken, June 12, 2024. JPEG The authors would like to express their gratitude to all of the individuals who have contributed to the collection of this data, specifically the following current and former USGS staff: Dave Naftz, Thomas Chapin, Tom Cleasby, August Schultz, Chris Ellison, Hannah Nilges, David Lange, Travis Schmidt, Greg Clark, Peter Wright, Jonathan O’Connell, Melissa Schaar, Ashley Bussell, Will Hamilton, Lindsey King, Molly Moloney, Madison Foster, Johanna Blake, Alex Walker, Rachel Hughes, Madison Goodman, and Scott Whiteman. Their willingness to spend long days working far from home through rain, snow, wind, fog, smoke, and a least one sandstorm made the collection of this data possible. Thanks are also owed to Dan Armstrong for working a holiday on short notice to assist with hauling out a boat and to Danie Frevola of Flathead Biostation for her willingness to assist USGS. We also thank Cailin Brugger and Sarah Newcomb for providing peer reviews of this data release. Lastly, we thank the many people in Eureka and Libby, Montana who have contributed to this project. These towns have become a second home to several of us on the Koocanusa project and we thank everyone there who has helped keep the Koocanusa monitoring crew lodged, fed, and supplied with all manner of hardware and services needed to produce this science. Kor 1.2.18.0 (YSI, 2022) was used to export data from the sonde used for field data collection. Data were processed using R 4.4.0 ( R Core Team, 2024) running on Windows 11. U.S. Geological Survey 2015 publication : U.S. Geological Survey Techniques of Water-Resources Investigations Book 9 Reston, VA US Geological Survey https://doi.org/10.3133/twri09 F. D. Wilde 2006 publication Techniques of Water-Resources Investigations 09-A6.1 Reston, VA US Geological Survey https://doi.org/10.3133/twri09A6.1 YSI, a Xylem brand 2024 publication Yellow Springs, OH YSI, a Xylem brand https://www.ysi.com/file%20library/documents/manuals/exo-user-manual-web.pdf R Core Team 2024 4.4.0 application/service Vienna, Austria R Foundation for Statistical Computing https://www.R-project.org/ YSI 2022 1.2.18.0 application/service https://www.ysi.com/kor-software Data were collected in accordance with USGS procedures for collecting water quality data and are reported to the same level of accuracy as data published in the USGS Water Data for the Nation database (waterdata.usgs.gov/nwis). All data were examined by USGS staff; several values falling outside the expected range of values were removed. See processing steps for details. Data were checked for duplicated values; none were found. Data represent measured values for the published water quality parameters for each site at the time of collection. Data were only collected during field visits and do not represent a continuous time series. The data only represent conditions for the sites at which measurements were made and may not be representative of conditions at all locations in Lake Koocanusa. Not applicable Not applicable Data were collected in the field using a YSI EXO2 sonde equipped with sensors for measuring water temperature, specific conductance, dissolved oxygen, pH, turbidity, and chlorophyll relative fluorescence as well as the depth of the sonde below the water surface. Following the methods described in the USGS National Field Manual (U.S. Geological Survey, 2015), the specific conductance, pH, and turbidity sensors were checked for calibration in the laboratory before each field trip and recalibrated as needed. The dissolved oxygen sensor was checked for calibration at the first field site of each trip and recalibrated as needed. Details on procedures for sensors for each parameter are provided in individual chapters of the National Field Manual. The temperature sensor was checked annually against National Institute of Standards and Technology calibrated thermometer following the guidance of Wilde (2006). The results of each calibration were recorded from the YSI Kor software and saved in the calibration records for the sonde. At the end of each field season, the sonde was sent to an independent laboratory for maintenance and checks on all the sensors. Water quality profiles at each site were collected by lowering the sonde through the water column while the sonde recorded data at intervals of 5 seconds or less. Before each profile, the sonde was held in the water within 1 meter of the surface to allow the sensor readings to stabilize before starting the profile. For each profile, the sonde was lowered at a rate such that the sensor readings would be reasonably stable at each recorded depth. Once the sonde reached the bottom of the lake, it was quickly raised to the surface. Data collected while raising the sonde are not published, as the sonde was frequently raised too quickly for the sensor readings to stabilize at each recorded depth. After collecting each sonde profile, the data from the sonde were downloaded to a computer and were exported as comma-separated value (.csv) files using the YSI KOR software (YSI, 2022). 2024 The exported data files were processed using R 4.4.0 (R Core Team, 2024). Only data collected while the sonde was lowered through the water column are included in this data release. Data with a depth of less than 1 meter (m) were removed. Data within 1.5 m of the deepest depth of the profile were also removed, as some of these contained erroneous readings affected by the sonde disturbing the bottom of the lake. The turbidity data at site 12301919 for May 18, 2021 were removed as the turbidity sensor did not appear to be reading correctly for that profile. Five data points were removed from the profile at site 12301919 on June 21, 2021, as they had very high turbidity readings, indicating they were likely affected by the EXO contacting the bottom of the lake even though they were more than 1.5 m above the greatest depth recorded for the profile, presumably due to lag in the reading from the depth sensor. Water quality data were rounded to the precision reported by the USGS Water Data for the Nation database (waterdata.usgs.gov/nwis) for each parameter. All turbidity data with raw values less than the 0.3 FNU accuracy limit of the turbidity sensor (YSI, 2024) are published as 0.3 with a "less than" qualification code. All chlorophyll relative fluorescence values less than 0.1 are published as 0.1 with a "less than" qualification code. 20241227 Vector Entity point 10 LakeKoocanusaProfiles_2024.csv Comma-separated values (CSV) file containing data. Producer Defined site_no U.S. Geological Survey site identification number USGS Water Data for the Nation https://waterdata.usgs.gov/nwis 12297500 Lake Koocanusa above Elk River, near Baynes Lake, British Columbia; located at 49.2289722, -115.261986 USGS Water Data for the Nation https://waterdata.usgs.gov/nwis 12299600 Lake Koocanusa below Elk River, near Grasmere, British Columbia; located at 49.1157444, -115.220986 USGS Water Data for the Nation https://waterdata.usgs.gov/nwis 12300110 Lake Koocanusa at international boundary; located at 48.98963056, -115.1809694 USGS Water Data for the Nation https://waterdata.usgs.gov/nwis 12301600 Lake Koocanusa below Pinkham Creek near Rexford Montana; located at 48.8269061, -115.2671173 USGS Water Data for the Nation https://waterdata.usgs.gov/nwis 12301830 Lake Koocanusa at Tenmile Creek near Libby, Montana; located at 48.58495918, -115.2321101 USGS Water Data for the Nation https://waterdata.usgs.gov/nwis 12301919 Lake Koocanusa at forebay, near Libby, Montana; located at 48.4140833, -115.3083056 USGS Water Data for the Nation https://waterdata.usgs.gov/nwis 485921115105901 Lake Koocanusa, right thalweg near 12300110; located at 48.9892, -115.183 USGS Water Data for the Nation https://waterdata.usgs.gov/nwis 485927115103401 Lake Koocanusa, left thalweg near 12300110; located at 48.9908, -115.176 USGS Water Data for the Nation https://waterdata.usgs.gov/nwis 485931115101601 Lake Koocanusa, lower bench near 12300110; located at 48.9919, -115.171 USGS Water Data for the Nation https://waterdata.usgs.gov/nwis 485936115095401 Lake Koocanusa, upper bench near 12300110; located at 48.9932, -115.165 USGS Water Data for the Nation https://waterdata.usgs.gov/nwis date Date on which data were collected Producer Defined 10/03/2019 12/11/2024 YYYY-MM-DD time Time at which data were collected, in Mountain Standard Time Producer Defined 07:53:56 20:24:07 HH:MM:SS Depth_m Depth of observation Producer Defined 1.00 101.79 meters Temp_C Temperature, water, degrees Celsius Producer Defined 0.8 24.3 degrees Celsius SpecCond_us_cm Specific conductance, water, unfiltered, microsiemens per centimeter at 25 degrees Celsius Producer Defined 185 359 microsiemens per centimeter DO_mg_l Dissolved oxygen, water, unfiltered, milligrams per liter Producer Defined 5.3 13.3 milligrams per liter pH pH, water, unfiltered, field, standard units Producer Defined 7.4 9.1 pH units Turb_FNU Turbidity, water, unfiltered, monochrome near infra-red LED light, 780-900 nm, detection angle 90 +-2.5 degrees, formazin nephelometric units (FNU) Producer Defined << empty cell >> No Data Producer Defined 0.3 94.1 formazin nephelometric units (FNU) Chloro_RFU Chlorophyll relative fluorescence, water, in situ, relative fluorescence units (RFU) Producer Defined 0.1 2.3 relative fluorescence units (RFU) Turb_FNU_cd Turbidity FNU qualification code Producer Defined L Observation is less than indicated value Producer Defined R Observation has been removed Producer Defined A Data are approved for publication as-observed Producer Defined Chloro_RFU_cd Chlorophyll RFU qualification code Producer Defined << empty cell >> No qualification code Producer Defined L Observation is less than indicated value Producer Defined A Data are approved for publication as-observed Producer Defined U.S. Geological Survey - ScienceBase mailing address

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Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Digital Data https://doi.org/10.5066/P143QAKP None 20250313 Seth Siefken U.S. Geological Survey Wyoming-Montana Water Science Center Hydrologist mailing and physical

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Helena MT 59601 USA 406-475-4626 ssiefken@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998