The Macro Invertebrate chart shows the organisms that are sensitive, somewhat sensitive, and tolerant to pollution. If mostly sensitive organisms are found, the water that is being tested is excellent. If only tolerant organisms are found, then the water quality is bad.
Sensitive Somewhat Sensitive Tolerant
Sample Bio-Indicator Form
After the Macro Invertebrate sample is collected, a bio-indicator form is completed. To fill in the form, the letters A, B, and C are used to represent the number of macro invertebrates present. A represents 1-9 macro invertebrates, B is used to represent 10-99 macro invertebrates, and C is for a 100 or more macro invertebrates. Each sample is collected in a 3 foot by 3 foot area. Then the letters are added up in each column and multiplied by the indicated value. The sensitive column is multiplied by three, the somewhat sensitive total is multiplied by two, and the tolerant is multiplied by one. Then all the index values are added together to get a total index value. The total index value is then compared with other water quality ratings. Excellent is indicated with a value greater than 22, good is between 17 and 22, fair is found between 11 and 16, and a poor rating is a total index value less than 11.