US Geological
  Survey logo

Water-Quality and Algal Conditions in the Clackamas River Basin, Oregon, and their Relations to Land and Water Management
By Kurt D. Carpenter
Water-Resources Investigations Report 02-4189
  Download the report
Report cover


In 1998, the U.S. Geological Survey sampled the Clackamas River, its major tributaries, and reservoirs to characterize basic water quality (nutrients, dissolved oxygen, pH, temperature, and conductance), water quantity (water sources within the basin), and algal conditions (biomass and species composition). Sampling locations reflected the dominant land uses in the basin (forest management, agriculture, and urban development) as well as the influence of hydroelectric projects, to examine how these human influences might be affecting water quality and algal conditions.

Nuisance algal growths, with accompanying negative effects on water quality, were observed at several locations in the basin during this study. Algal biomass in the lower Clackamas River reached a maximum of 300 mg/m2 chlorophyll a, producing nuisance algal conditions, including fouled stream channels and daily fluctuations in pH and dissolved oxygen concentrations to levels that did not meet water-quality standards.

Algal biomass was highest at sites immediately downstream from the hydroelectric project's reservoirs and/or powerhouses. Nuisance algal conditions also were observed in some of the tributaries, including the North Fork of the Clackamas River, Clear Creek, Rock Creek, and Sieben Creek. High amounts of drifting algae increased turbidity levels in the Clackamas River during June, which coincided with a general increase in the concentration of disinfection by-products found in treated Clackamas River water used for drinking, presumably due to the greater amounts of organic matter in the river.

The highest nutrient concentrations were found in the four lowermost tributaries (Deep, Richardson, Rock, and Sieben Creeks), where most of the agriculture and urban development is concentrated. Of these, the greatest load of nutrients came from Deep Creek, which had both high nutrient concentrations and relatively high streamflow. Streams draining forestland in the upper basin (upper Clackamas River and Oak Grove Fork) had the highest concentrations of phosphorus (and lowest concentrations of nitrogen), and streams draining forestland in the middle basin (Clear Creek, Eagle Creek, and the North Fork of the Clackamas River) had relatively high concentrations of nitrogen (and low concentrations of phosphorus). In contrast, relatively low concentrations of both nitrogen and phosphorus were found at the two reference streams, reflecting their pristine condition. Relatively high phosphorus levels in the upper basin are probably due to the erosion of naturally occurring phosphorus deposits in this area. Likely sources of nitrogen (mostly nitrate) in the forested watersheds include nitrogen-fixing plants, atmospheric deposition, timber harvesting, and applications of urea fertilizers.


Executive Summary
    Study Background and Objectives
    Overview of the Clackamas River Basin
    Data Collection
    Data Quality Control
    Data Analysis
    Stream Conditions
    Reservoir Conditions
    Ground-Water Conditions
    Relations between Land Use and
      Nutrient and Algal Conditions
    Effects of Hydroelectric Projects on
      Stream Conditions
    Stream Nutrient Conditions
    Comparison of Nutrient Concentrations
      to Suggested Criteria
    Nutrient Sources in the Clackamas River Basin
    Algal Conditions in Streams
    Algal Conditions in Reservoirs
    Effects of Algal Blooms on Drinking Water
    Land Use and Water Management
      in the Clackamas River Basin
    Evaluation of Management Strategies
      to Improve Conditions
    Information Needs and Potential Future Studies Conclusion
References Cited

Download the report (PDF, 5 MB) (Adobe PDF Reader required; version 5 or higher preferred.)
If you do not have the Adobe PDF Reader, it is available for free download from Adobe Systems Incorporated.
Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by screen-reading programs that synthesize text as audible speech. In addition, a version of Acrobat Reader 6 that contains support for screen readers is available. The conversion tools and the accessible reader may be obtained free from Adobe at Access Adobe.

Order a printed copy of this or other USGS water-resources reports.
For information about the Clackamas River Water-Quality study, please visit the project Web site.
To find out more about the USGS in Oregon, please visit our home page.

[an error occurred while processing this directive]

FirstGov button  Take Pride in America button