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from the Regions:

Montana Department of Environmental Quality to Complete Algal Perception Study

The Montana Department of Environmental Quality (MDEQ) is currently completing work intended to evaluate people’s perceptions of algal levels in Montana’s wadeable rivers and streams.  MDEQ surveyed a randomly selected group of Montana residents, as well as a group of resident and non-resident river and stream users, to determine whether those surveyed believed various algal levels were desirable or undesirable in relation to their recreational use of these waterbodies.  Montana’s waterbodies are all classified, with recreation (including swimming and bathing) as a designated beneficial use.   The intent of this work was to clarify the relationship between stream-bottom algal density and support of the recreation beneficial use. 

What approach did you take in developing this study?

• MDEQ first developed the following two questions:

1. What density of algae in wadeable streams and rivers is high enough that Montanans perceive that it will interfere with their recreational use in or on the water?
2. For recreational users of wadeable streams and rivers in Montana, what density of algae is high enough that they perceive that it will interfere with their recreation in or on the water?

• A rigorous statistical design was then used to develop two surveys, each addressing one of the questions and its associated group (i.e., population). The questions were concerned with finding the level of algae that is high enough to be perceived to interfere with recreation in or on the water, if such a level exists.   The sample frame for the first question was registered Montana voters, which, based on a 2004 Census Bureau estimate, represents about 85% of the voting-age population of the state.  The sample frame for the second question was individuals who researchers observed recreating on a randomly-selected group of Montana river and stream segments. It is important to note that the two groups are not mutually exclusive. 

• MDEQ, in cooperation with the University of Montana, finished a by-mail survey with the group of randomly-selected registered Montana voters in August, 2006.  They are currently completing their non-respondent follow-up plan.  For the second group, two University of Montana students conducted face-to-face interviews on the state’s wadeable rivers and streams from June to August, 2006. 

• For both the by-mail and on-river surveys, people were presented with a series of eight photos (laid out in a pre-established random order), which showed different levels of benthic algae. The algal levels presented spanned the range of algae densities that have been measured in rivers and streams across the state.  Both groups were then solicited for one of two possible responses to each photo; desirable or undesirable.

What are the future plans for this work?

The response data collected will be binomial in distribution (either desirable or undesirable), and MDEQ will be able to place confidence limits (e.g., 95%) and confidence intervals (e.g., ± 5%) around the responses to each photo.  The results of the two surveys, compiled in a final report, should be ready in late 2006 or early 2007, and is intended to be posted on the web.

What are the regulatory implications of this work?

The results should provide an unbiased evaluation of the public’s tolerance for benthic algae in this part of the country, and MDEQ hopes to be able to identify a threshold beyond which algae levels are no longer acceptable for recreation.  This in turn will help MDEQ with its ongoing development of numeric nutrient criteria.  

For more information, please contact Michael Suplee, MDEQ Water Quality Standards Section, at: msuplee@mt.gov.