Enter the count of each taxon you identified. Leave at 0 if absent. Tolerance values (TV) are family-level scores per Hilsenhoff (1988) and Bode (1988).
| Family / Taxon | Common Name | TV | Count |
|---|
Estimates for guidance only — not a substitute for certified laboratory analysis. FBI is calibrated for North American temperate streams (Hilsenhoff 1988). US EPA RBP protocols
How to Use This Calculator
- Fill in site details (optional but useful for the printout — stream name, date, substrate type, and sampling gear).
- Enter your count for each taxon group you found in the sample. Use 0 for absent taxa. The tool covers the most common families encountered in North American kick-sampling.
- Read the results instantly — FBI score and rating, EPT index percentage, taxa richness, Shannon diversity, and EPT:Chironomid ratio all update as you type.
- Check sample adequacy — the banner shows whether your total count meets the recommended 100-organism threshold for reliable FBI calculation.
- Export or print your results as a clean summary PDF or CSV for field records.
Understanding the Indices
Hilsenhoff Family Biotic Index (FBI)
Developed by William L. Hilsenhoff at the University of Wisconsin–Madison, the Family Biotic Index is the most widely used rapid bioassessment metric in North America. It weights each organism's count by its family's known pollution tolerance (0 = very intolerant, 10 = very tolerant), then divides by total count:
A sample dominated by sensitive stoneflies and caddisflies gives a low FBI (good quality); one dominated by tubificid worms and midges gives a high FBI (poor quality).
| FBI Score | Water Quality | Degree of Pollution |
|---|---|---|
| 0.00 – 3.50 | Excellent | No apparent organic pollution |
| 3.51 – 4.50 | Very Good | Possible slight organic pollution |
| 4.51 – 5.50 | Good | Some organic pollution |
| 5.51 – 6.50 | Fair | Fairly significant organic pollution |
| 6.51 – 7.50 | Fairly Poor | Significant organic pollution |
| 7.51 – 8.50 | Poor | Very significant organic pollution |
| 8.51 – 10.00 | Very Poor | Severe organic pollution |
EPT Index
Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) are collectively called EPT — the three orders most sensitive to organic pollution and low dissolved oxygen. EPT% = (total EPT individuals / total sample) × 100. Healthy streams typically exceed 50% EPT; degraded streams often fall below 10%.
Shannon Diversity Index (H′)
Shannon H′ captures both richness (number of taxa) and evenness (how evenly individuals are spread). For stream macroinvertebrates, H′ above 2.5 typically reflects a diverse, healthy community; values below 1.0 suggest dominance by a few tolerant taxa.
EPT : Chironomid Ratio
Chironomid midges (family Chironomidae) are highly tolerant generalists. A high EPT count relative to chironomids is a sign of clean-water conditions. In impaired streams, chironomids often make up 50–80% of all individuals while EPT taxa nearly disappear.
When to Use Kick-Sampling
Kick-sampling is best conducted during stable base-flow — avoid sampling within two weeks of heavy rain or snowmelt, which scours organisms downstream. Most North American rapid bioassessment protocols designate spring or early autumn as index periods. Riffle habitats over cobble substrate yield the most representative communities and are the standard target for FBI calculation. Always sample upstream first and work downstream to avoid disturbing your sample site.