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Discovering a Problem in Maine

Program History and Overview

In 1983, the Maine Department of Environmental Protection (DEP) began using a standardized sampling protocol to assess benthic macroinvertebrate stream communities. Since then, many sites, including reference sites, have been sampled and the information has been compiled in a standardized database. The development of this database allowed statistical analysis of the biosurvey data to support revision of the water classification standards, which was accomplished in 1986. (The condition of the aquatic community, levels of dissolved oxygen, and numbers of bacteria are the three major standards in the water quality classification law).

The DEP uses 30 measures to assess macroinvertebrate data, including HBI, generic richness, Ephemeroptera- Plecoptera-Trichoptera (EPT), and Ephemeroptera- Plecoptera (EP). Statistical analysis of the data produces a list of probabilities of meeting the criteria for Class AA, A, B, and C. The numeric biocriteria are used as thresholds to judge whether aquatic life uses are being attained. The final determination of attainment is made following review of data and site-specific conditions by an expert biologist. 

Biological Standards for Maine's Classes of Water Quality for Rivers and Streams
Class Biological Standard
AA Habitat natural and free flowing. Aquatic life as naturally occurs.
A Habitat natural. Aquatic life as naturally occurs.
B Habitat unimpaired. Ambient water quality sufficient to support life stages of all indigenous species. Only non-detrimental changes in community composition allowed.
C Ambient water quality sufficient to support life stages of all indigenous fish species. Change in community composition may occur, but structure and function of community must be maintained.

Although full development of Maine's bioassessment database took many years, data were used at the beginning of the process to revise the water quality standards. In addition, some of the earliest biosurvey data collected were used to reveal problems that were not previously evident.

Biosurvey Results Point to a Problem

The East Branch of the Sebasticook River at the town of Corinna formerly received a permitted Publicly Owned Treatment Works discharge, which was approximately 70% wastewater from a woolen mill. A routine benthic invertebrate survey in 1983 (before implementation of biocriteria) found only 11 individual organisms, from four genera. (According to current data, an average of x-y organisms and z genera is expected in samples from healthy sites.) The impairment in this case was obvious and did not require the use of the statistical model that was developed a decade later and is important in more subtle cases. The biosurvey results at this site were surprising, because no permit limits were violated and chemical sampling showed no evidence of water quality problems.

The results of the biomonitoring triggered a series of actions to identify and correct this problem, which was previously unrecognized. An evaluation of whole effluent toxicity demonstrated that the effluent was quite toxic (no- observable-adverse-effect-level less than 1%). Between 1983 and 1988 in spite of aggressive toxicity reduction efforts, poor effluent quality continued to be reflected in the character of the instream community. In 1988, the total abundance of individuals averaged 9 per sampling device with a generic richness of 11 across the three samples collected, indicated the site still failed to attain the minimum standard for class C waters (and for the statistical model).

Investigation by the woolen mill indicated that interactions between the constituents of the mill's discharge and the chlorine added at the POTW was causing the toxicity in the final effluent. Process changes at the mill, dechlorination at the POTW, and a dramatic reduction in effluent BOD ultimately resulted in decreased toxicity of the final effluent. By 1989, just four months after dechlorination was instituted, the benthic macroinvertebrate community had improved to the extent that the minimum provisions for numbers and richness were being met. The results of sampling conducted in 1990 indicated additional improvement, with 1,234 individuals per sampler and a generic richness of 24. In addition, the presence of pollution-sensitive organisms increased, as indicated by the EP and EPT indices. The biomonitoring results indicated that the macroinvertebrate community responded favorably to improved effluent quality.

Lesson Learned

The use of biocriteria in Maine's program revealed a water quality problem in the Sebasticook River, even though the discharger was in compliance with all permit limits.

Additional Information

Susan Davies ( at Maine DEP at 207-287-7778. You can also visit the Maine website Exit.


Davies, S.P., L. Tsomides, D. Courtemanch, and F. Drummond, 1995. Maine Biological Monitoring and Biocriteria Development Program. Maine Department of Environmental Protection. Augusta, ME. 61 pgs.

Davies, S.P., L. Tsomides, J. DiFranco, and D. Courtemanch, 1999. Biomonitoring Retrospective: 15 Year Summary for Maine Rivers and Streams. Maine Department of Environmental Protection. Augusta, ME. 190 pgs.

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