Bighorn River Water Quality near Fort Smith, Montana

Overview

The Bighorn River near Fort Smith, MT, has relatively good water quality and the river is an important coldwater fishery for anglers. In recent years, trout numbers per mile have declined due, in part, to high flows in 2017 and 2018 (Montana Department of Fish, Wildlife, and Parks). Water temperature and specific conductance, monitored continuously by the U.S. Geological Survey (USGS—water temperature only) and Bureau of Reclamation (BOR—water temperature and specific conductance), tend to track with air temperatures near the sampling location (see water temperature graphs below).

Dominant cations at the sampling location on the Bighorn River are calcium and sodium. Dominant anions are bicarbonate and sulfate. Relative to the Bighorn River near Kane, WY, there was a limited amount of variation in measured analytes in 2019. Reservoir storage and subsequent dam releases contribute to this result as well as the low variation in suspended sediment levels across the year. In unregulated rivers, suspended sediments and total phosphorus are typically at their annual maxima during high flows. However, dam operations prevent much sediment and associated phosphorus from entering the reach of river below the dam. Other analytes (e.g., sulfate, total calcium, and total sodium) are at their annual minima during high flows and typically increase as flows drop. Levels of nitrate-nitrogen and total phosphorus in the Bighorn River near Fort Smith, MT, were 0.36 mg/L and 0.02 mg/L, respectively in 2019. Ammonia nitrogen levels were below detection levels (i.e., <0.05 mg/L) on all sampling occasions. Recommended nutrient criteria for this Montana ecoregion is 1.3 mg/L total nitrogen and 0.15 mg/L total phosphorus (See Montana Department of Environmental Quality 2013 in Article 5 of this series).

Summary of daily maximum water temperature (top) and daily average water temperature (bottom) in the Bighorn River near Fort Smith, MT (USGS Gage 06287000). NPS

Daily air temperature range, river discharge, and water quality data for 2019 from U.S. Geological Survey (USGS) and Bureau of Reclamation (BOR). NPS

2019 Water Quality Lab Results

The following table contains quarterly water quality lab results for the Bighorn River near Fort Smith, MT. Download tabular data here for these tables.

Table 1. Quarterly water quality lab results (in mg/L) for Bighorn River near Fort Smith, MT. All samples were processed at Energy Laboratories in Billings, Montana. Reporting limit (in mg/L) is the threshold value that many analytical labs consider to be the lowest reportable value for an individual analyte; this value may be higher than the maximum detection limit. ND = non-detectable result. Some sampling events included a blank sample where indicated; blank samples are processed using certified inorganic free deionized water.

2019 Water Quality Field Results

Download tabular data here for this table.

Table 2. Summary of quarterly field parameter results for Bighorn River near Fort Smith, MT.

More Data

Data prior to 2016 are available at the Water Quality Portal using BICAWQ01 for the project and 11NPSWRD_WQX-BICA_BHR1 as the site identifier for the Bighorn River near Fort Smith, MT.

Part of a series of articles titled
Water Resources Monitoring in the Bighorn River near Fort Smith, Montana, 2019.

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Water Flow in the Bighorn River near Fort Smith, Montana

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Monitoring Methods for the Bighorn River near Fort Smith, Montana

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• Bighorn Canyon National Recreation Area

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