A Field Investigation of Crescent Bay Lake

DRAFT - Comments and recommendations welcome.


On July 19, 2012, teachers in The River Mile expansion workshop conducted field investigations in the area of Crescent Bay and Crescent Bay Lake. Help the teachers complete their investigation.

Questions: How do the water quality parameters of pH, dissolved oxygen, conductivity and temperature vary by depth in Crescent Bay Lake?

Background: According to a 1983 State of Washington Dept. of Ecology report, Crescent Bay Lake was formed by "diking an arm of Franklin D. Roosevelt Lake" (Water Quality of Crescent Bay Lake - Pub. 83e18). At that time, the lake was reported to have two inlets. One was a City of Grand Coulee effluent stream of primary treated domestic sewage. The other was Bureau of Reclamation irrigation water pumped into the lake from Lake Roosevelt. The city waste has since stopped and efforts have been made to clean the lake. The one outlet to the lake is a culvert at the north end that empties into Lake Roosevelt at Crescent Bay.

Efforts have been made to develop the Crescent Bay area, including Crescent Bay Lake for recreational use. Many of these plans have fallen through. (For more information regarding the area, see Ch. 7 of Lake Roosevelt Administrative History: South Marina & Crescent Bay.)

The use of Crescent Bay Lake for recreation will depend largely on its water quality. In turn, its water quality and functioning as an aquatic system is going to be affected by its geographic conditions (depth, temperature and rainfall patterns, surrounding geology, ...) and impacted by human activity (past and present). These influences will affect the lake's physical (temperature, substrate, turbidity, ...), chemical (pH, dissolved oxygen, organic nutrients, conductivity, ...) and biologic (bacteria, plankton, plant & animal communities, ...) conditions.

For example, the lake's past history as the outlet for the city of Grand Coulee's treated waste water suggests the lake could have an abundance of organic matter (nutrients). This could increase plant, algae and phytoplankton growth. It could also increase the activity of bacteria (breaking down the organic matter) and use up dissolved oxygen in the water. Temperature also affects the concentration of dissolved oxygen. Colder water has a higher capacity for dissolved oxygen, while warmer waters become saturated at lower levels. However, deeper lakes do not mix well. Warmer water at the surface floats above the colder, denser waters below during the summer, thus creating layers (stratification). This means that dissolved oxygen near the bottom of the lake will not get replenished easily. All of this has a direct effect on the organisms (fish and aquatic invertebrates) in the lake that depend on dissolved oxygen for survival. These organisms are additionally affected by other water quality parameters such as as temperature and pH.

(For more info see: Physical Character & Water Quality of Lakes - WA Dept. of Ecology)

Background Documents:

labeled lake image
Google maps

lake depth map
fortress.wa.gov (pdf)

lake depth map

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Hypothesis: The water quality paramenters of temperature, dissolved oxygen, pH, and conductivity for Crescent Bay Lake will change for different depths within the lake. The water temperature will get colder at greater depth due to the absorption of solar energy at the surface and density differences in the water resulting in stratification. Dissolved oxygen will decrease with depth as a result of decomposition of organic material at the bottom of the lake and increased distance from the lake's surface where oxygen transfer with the air occurs. (DO in Lake - WA Dept. of Ecology) The pH value will decrease with depth, indicating an increase in acidity. This results from photosynthesis near the surface and decomposition at depth. (pH in Lakes - WA Dept of Ecology) The change in conductivity is uncertain. Conductivity decreases as temperature decreases, but it increases with an increase in chloride, phosphate, and nitrate that can result from decomposition of organic matter. (Conductivity - US EPA) Therefore, if the YSI instrument compensates for the change in temperature, the conductivity is likely to increase with depth. If not, then, the temperature could have a greater influence and the conductivity will decrease.

(Note: This is not a typical hypothesis for students. While data on multiple variables is often collected during field investigations, students should limit the focus of their reports -- and their answers to the questions below -- on one or two of the measured variables.)

Procedure: Measurements will be taken of the lake's temperature, DO, pH, and conductivity at different locations and depths (surface, 5 m, 10 m) in Crescent Bay Lake. For this, a YSI instrument with a 10 meter cable & sensor will be used, and the instrument will be calibrated before taking the readings. (Thanks, Adam!). The lake's clarity (turbidity) using a Secchi disk at each of the locations will be determined, as well. The location on the lake for each set of measurements will be obtained by using a GPS device. Data will be recorded on-site for each location and for each depth at the time of sampling.

The results of our investigation can be found in the table, chart, images, and ArcGIS map below:

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Data & ArcGIS map
water quality data (open source
CBL_data_final (OpenDoc)
CBL_data_final (.pdf)

water quality data chart
CBL_data_chart1 (.pdf)

water quality sampling locations (labels added to picture using Adobe Photoshop Elements)

lake image
Google maps

Crescent Bay Lake (CBL)
water quality data...
OpenDoc format:
CBL_data (.ods)

comma delimited files:
CBL_data-all (.csv)


Click image above to view ArcGIS map
screen capture of data (CBL_data-all.csv) imported into ArcGIS Explorer

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Assignment 1

Help the teachers complete their investigation by completing the following ...

  1. What were the variables in the investigation? What type of investigation do you think this was -- descriptive, comparative, or correlative. (Explain)
  2. Make your own graph that compares (one) or attempts to correlate (two) variable(s) in the investigation.
  3. Describe the results (data) of the investigation. (What happened to the measurements as the depth increased from the surface, 5 meters, and 10 meters.)
  4. Was the hypothesis of the investigation correct? How do you know? (Support your conclusion with data.)
  5. Provide an explanation for the results? (Choose one or two variables and make an inference about why the variable(s) changed.)
  6. Do you think the investigation was a "fair" test of the lake's water quality? What are some limitations or possible sources of error in the investigation?
  7. What recommendations would you make for improving or extending this investigation?
  8. What recommendations would you have for managing the lake based on these results. Or, what effect do you think these results might have on other parts (biotic/abiotic) of the lake system?

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Assgnment 2

Use ArcGIS Explorer to complete the following ...

  1. Download and save the spreadsheet file CBL_data-all.csv (Note: data needed to be rearranged in the spreadsheet in order to show all data for all depths at each location; also, this spreadsheet file must be closed before it can be imported into ArcGIS.)
  2. Create an ArcGIS Explorer map for Crescent Bay Lake, Grant Co., WA (ArcGIS Explore Online)
  3. Select to import the .csv data into the ArcGIS map ("Add Content" | "Import" | "Create features from .csv file" | "Browse for file" ... [CBL_data-all.csv] | "Open" | "Next" | "Import")
  4. The four locations should now appear on your map of Crescent Bay Lake. Click on the points and view the data in the Pop-up windows. What similaries and differences do you see in the data? (Make two observations (patterns/changes) and support your observations with specific values.)
  5. Use the "Measure" tool to determine the perimeter of the polygon formed by contecting the four locations (A-B-C-D).
  6. Use the "Measure" tool to determine the surface area of the lake enclosed by these four points?
  7. Select "Pushpin" from the "Add Features" tab and create two additional locations where you recommend additional water quality data be collected. Record the latitude (N/S) and longitude (E/W) for these locations. To find the coordinates...
    1. select the "Measure" tool
    2. choose the "Get the location of a point" option
    3. click on the desired location on the map (change coordinates format, as needed)
    4. the coordinates can be copied to another application or document using the "Copy measure value to clipboard" option**
    5. move your cursor over the compass image in the lower left corner of the ArcGIS Explorer window and select "Show Coordinates." Now, move your cursor over the two pushins you added to the map.) Why did you choose these additional locations?
    **Hint: Here's how to make a "New layer" from a series of locations in an ArcGIS map:
    1. use the "Copy measure value to clipboard option" to paste a list of coordinates from the ArcGIS map into Word or Notepad
    2. remove the "degree" symbol (Find/Replace)
    3. optional: add a number or name for each location before each coordinate (such as: 1, 2, 3, ...), followed by a comma
    4. at the top of the list, add a new line with the headings: "location (or some other label for the points if you followed optional step 3), latitude, longitude" (include the commas to seperate the values)
    5. save the file in plain text (.txt) format (your file name will become the name of the new layer in ArcGIS)
    6. CLOSE the file (otherwise, you may not be able to Import)
    7. back in ArcGIS, use the "Add content" tool | "Import" | "Create features from a .csv file" | "Browse for a file" | next to the "File Name" box change from "CSV Files (*.csv)" to "Text Files (*.txt) | find the file and "Open" | "Next" | "Import"
    8. All your points have been imported and are now in a new layer.
    9. Other information could be added to the text file, as well. Put a label for the information in the top line (along with "latitude, longitude") and add a comma to seperate the "fields" of information

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Notes to other educators on a budget using PC's:

1. If you have information (text, documents, charts, ...) that you need to make into JPG images, try selecting & copying them into Windows Paint (found in the accessories folder). Using the Paint program, I was able to copy/paste a chart I made in Excel into Paint, and then save as a JPG file. I couldn't find a "Save as..." or "Export" feature that would let me do that directly in Excel. There are other image editing programs that will allow you to do this, but I was looking for something already available on my computer.

2. I found a handy screen capture utility that I didn't know was on my computer, it is called Snipping Tool (found in the accessories folder, or go to the Start Button and type "snip"). In capturing the lake depth map from a .pdf document I found online, I was able to use the Snipping Tool and save the map as a JPG image.

3. Although I usually use Photoshop Elements for editing (adjusting contrast & resizing) images, I found that MS Office Picture Manager also works. I resized many of the images you see on this page using the Picture Manager program.

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Lake Roosevelt (top)
& Cresent Bay Lake

Crescent Bay (top)
& Crescent Bay Lake

Crescent Bay Lake
at waterfalls
West shoreline - location D

Crescent Bay Lake
NW shoreline - location A

Crescent Bay Lake

Crescent Bay Lake at
outlet culvert

outlet culvert & canoe launch

Crescent Bay Lake at
outlet culvert

Crescent Bay Lake at canoe launch

Crescent Bay Lake
looking to N end of lake

Crescent Bay Lake looking SW from north end of lake
(canoe launch point & outlet culvert on right)

Crescent Bay Lake
looking to N end of lake

Adam with YSI water quality monitoring instrument

Carol with canoe

Mike with Secchi disk

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Lake Roosevelt National Recreation Area website
Lake Roosevelt Visitor Guide
(May - June 2012) - Information on the Lake Roosevelt National Recreation Area

Note: The images above were taken with an Olympus SZ-10. They were then cropped and enhanced (lighting & contrast) in Adobe Photoshop Elements and/or other image editing software.

Created by Michael R. Clapp (2012). All rights reserved.
For more information, contact: mclapp@nwnature.net

updated: 8/7/12