How the Public Views Nuisance Algae in Montana Streams

by Heather McKee, Vicki Watson (University of Montana), and Michael Suplee (MT Dept of Environmental Quality)

January 2007


During the summer of 2006, the University of Montana Watershed Health Clinic, working with the Montana Department of Environmental Quality, conducted two surveys to evaluate the public’s perceptions of stream bottom algae levels in Montana’s rivers and streams. Because algae levels are strongly tied to nutrient concentrations in water, information gathered on public opinions of algae levels through these surveys may be used to help shape acceptable nutrient concentration standards for Montana’s rivers and streams.


Two surveys were conducted to assess public opinion. An On-River Survey was performed along rivers and streams throughout the state, obtaining responses from 563 river recreationists. A By-Mail Survey of registered Montana voters was also performed, receiving responses from 433 Montana residents. The streams and rivers visited during the On-River Survey, as well as the group of registered Montana voters solicited for the By-Mail survey, were chosen randomly.

Respondents looked at eight photographs of Montana rivers and streams, each representing a different level of stream bottom algae. Photographs were presented in random order for the surveys. For each photograph, respondents decided if the level of algae shown would be “desirable” or “undesirable” for their major form of recreation on rivers and streams.

To see the algae photos used in the survey, scroll down to bottom of this page. Note that the measure of stream bottom algae used here is the amount of the green pigment chlorophyll on the bottom of the stream (measured in the units of mg chlorophyll per square meter of stream bottom).

Results & Conclusion

Results are summarized in Figure 1 (note that the algae pictures which were presented to survey respondents in random order are arranged in order of increasing algae levels in this figure). The bars in Figure 1 represent the percentage of respondents who expressed that opinion. While the little 'error bars' (which look like an I ) on the bars represent our confidence in how well the people surveyed represent all Montana voters & river users. A statistician would say:
        "The error bars are +/- the 95% confidence level of the proportion of
        respondents who considered the level desirable, expressed as a percent."

In both the On-River and By-Mail Surveys, the public communicated a marked decline in desirability of a stream or river for recreation at chlorophyll levels of 200 mg/sq meter and higher. All chlorophyll levels at or above 200 mg/sq meter (represented by Photographs E, B, H, C and D) were determined to be “undesirable” by the majority of survey respondents in both groups surveyed. Chlorophyll levels at or below 150 mg/sq meter (represented by photos A, G, and F) were determined to be “desirable” by the majority of survey respondents in both groups surveyed.

Thus instream nutrient standards might be set at the concentrations associated with stream bottom chlorophyll levels around 150 mg/sq meter.

Figure 1



algae picture A IMAGE Aalgae picture BIMAGE B

algae picture CIMAGE Calgae picture D IMAGE D

algae picture DIMAGE Ealgae picture FIMAGE F

algae picture F IMAGE Galgae picture H IMAGE H