Water-Quality Monitoring of Canyon Lake

Executive Summary

Canyon Lake provides residents with areas for fishing, boating, and other recreation in Rapid City, South Dakota. The lake acts as a nutrient and sediment sink that allows for widespread aquatic plant growth within the lake, and the water also attracts a large waterfowl population. In order to better assess the sources of fecal indicator bacteria in Rapid Creek, more data is needed regarding the bacteria loading that occurs at Canyon Lake primarily due to waterfowl congregation. Very limited data for fecal indicator bacteria is available for Canyon Lake or Rapid Creek immediately below the dam. Currently, there is not a routine monitoring program that would be able to detect water-quality issues that may arise at Canyon Lake. Dredging of the lake is expected to begin in the year 2017, and is expected to benefit the lake by (1) improving aquatic habitat, (2) maintaining storage capacity, and (3) maintaining the water quality of Rapid Creek.

The U.S. Geological Survey will collect samples at specific locations on Canyon Lake and Rapid Creek prior to and after dredging activities. Sample locations will include Rapid Creek sites above and below Canyon Lake to assess water-quality changes that occur within Canyon Lake, and three sites on Canyon Lake. Water-quality information collected will include field parameters (pH, dissolved oxygen, temperature, specific conductance, Secchi disk depth, and turbidity), sediment, nutrients (nitrogen and phosphorus), total organic carbon, chlorophyll a, and fecal indicator bacteria (E. coli).  Water-quality data will be collected 16 times during a 2-year period to capture seasonal variations. Data collected from this project will be provided to the public on the National Water Information System website.

Objectives

The project contains two separate objectives, but a single approach. The first objective is to document any changes to Canyon Lake water quality that may occur following dredging. The second objective is to provide data that can be used to assess the amount of sediment, nutrient, and bacteria loading that occur within Canyon Lake.

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