Stream Indicator Species

Latest Score:


in 2019

Weight: 8%
score trend is up over time

The effectiveness of a forest in providing clean water is assessed through the diversity of key indicator species of stream health. A stream indicator species in this context is a macroinvertebrate (insects, worms, or snails) whose presence, absence, or abundance reflects the current condition of the environment. Macroinvertebrates typically require high levels of dissolved oxygen and low turbidity in the water. Here, we used the EPT species richness (a measure of the richness of sensitive taxa) of macroinvertebrates found at a monitoring site in Ranch Brook in Underhill, Vermont. High diversity indicates better habitat conditions and better water quality. A high score means that stream indicator species diversity is staying high over time.

While there is a slight positive trend in the richness of sensitive species (i.e. Ephemeroptera, Plecoptera, and Trichoptera taxa) at Ranch Brook over the last 19 years, richness values have stayed within a consistent range of 20-27 species. These values are typical of small, high-elevation, low productivity Vermont reference streams. Variation in richness values on a year-to-year basis can be affected by variability in environmental conditions, including flow regime. While it would not be expected that species richness would continue to increase significantly in this forested headwater stream, it is possible that increasing stream temperatures or extreme flood events associated with climate change could cause an eventual decline.

Interpretation provided by:

Aaron Moore, Environmental Scientist; Vermont Agency of Agriculture, Food and Markets (2020)


The score is calculated using a target value and the historical range of the the entire long-term dataset. The higher the score, the closer this year's value is to the target.

Once the score is computed for each year, the trend in scores over time is calculated. If the trend is significantly positive or negative, the long-term trend is marked as increasing or decreasing respectively.

Component Description
Scored as

Distance between 0 and target (scaled 1-5)

Target value

Data maximum + 10% of range

Directionality of scores

No change from the long-term mean is better.

Minimum value used in scoring


Maximum value used in scoring

Data maximum + 10% of range

Species richness was collected from the Vermont Integrated Watershed Information System1. We selected one location, Ranch Brook (site #502032) in Underhill VT, where species richness metrics were computed for macroinvertebrates. Data from other locations in the state did not have annually-resolved data with a sufficient long-term record to warrant inclusion. We used the EPT richness score as computed by the datasetauthors2. EPT richness is a count of the unique number of taxa identified in the sample that belong to a trio of particularly sensitive macroinvertebrate orders - Ephemeroptera (mayflies), Plecoptera (stoneflies), and Tricoptera (caddisflies). In cases where a specimen could not be identified to the species level, it was only counted as unique taxon if no other specimens were identified to that level or below. In some cases, there were multiple samples in a single year. In these cases, we took the mean of the EPT richness scores as the value for the year. The target for these data was set to be the maximum value plus 10% of the range. The annual score was computed as the difference between the lower scoring bound of 0 (indicating no EPT taxa were identified) and the target, scaled between 1 and 5.

1 VTDEC-Watershed Management Division. 2019. Integrated Watershed Information System (IWIS). Available at:
2 Vermont Agency of Natural Resources, Department of Environmental Conservation, Water Quality Division. 2012. Water Quality Field Methods. Available at: