Pennsylvania Water Science Center


Tammy Zimmerman


In cooperation with the Berks County Conservancy

Blue Marsh Lake — Results of a Pilot Study to Identify Sources of Bacteria

cow in pasture
(click thumbnail for larger image)
geese in lake
(click thumbnail for larger image)
Agricultural activity on tributaries may contribute to bacteria in Blue Marsh Lake. Geese may be a significant source of bacteria in Blue Marsh Lake.


Blue Marsh Lake was constructed in 1979 by the U.S. Army Corps of Engineers. It is located on the Tulpehocken Creek, a tributary of the Schuylkill River, approximately 6.4 miles upstream from Reading in Berks County, PA. Blue Marsh Lake provides the public with activities that include swimming, boating, fishing, water skiing, and sailing. Occasionally, fecal coliform concentrations in the lake have exceeded recreational water-quality standards.


The pilot study focused on the distribution of fecal contamination determined by measuring selected bacterial concentrations in the lake itself, the perennial tributaries that flow into the lake, and sand samples from the beach at the swimming area. Data were collected under baseflow and stormflow conditions.


During stormflow, there were higher numbers of fecal bacteria in the tributaries than in the lake. The data also showed elevated concentrations of the indicator bacteria in the sand at the swimming area.

Graph of fecal coliform concentrations

Fecal coliform concentrations in the tributaries, lake, water at the swimming area, and sand at the swimming area, September and October 2001. The bars represent the average of the individual samples for each area. Concentrations of organisms are based on samples of 100 mL for water and 100 grams for sand. The dashed line at 200 CFU represents the recreational water-quality standard for Pennsylvania. The line does not extend across the chart to the sand because Pennsylvania does not have a recreational standard for fecal coliforms in sand.

A USGS factsheet summarizes the results from the pilot study.

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