Teacher Notes

Stream Macroinvertebrate Sampling Simulation

Student Activity Kit

Materials Included In Kit

Stream Organism Sheet Sets, 2 laminated sheets per set, 10 different color sets

Additional Materials Required

Marker, dry-erase

Prelab Preparation

  1. Cut the organisms out from each different color laminated Stream Organism Sheet Set. Enlist the help of a student aide or have each group of students cut out their own set before beginning the activity.
  2. Place the cut out organisms for each set in separate plastic bags for storage.

Safety Precautions

Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.


The materials in this activity may be saved and reused for future classes.

Teacher Tips

  • Enough materials are supplied in this kit for 10 groups of students working in groups of three.

  • Students should rotate different color sets of organisms accordingly as described in Parts I and II of the Procedure.
  • The recommended target organisms for each set is as follows:

    1 (Blue) Backswimmer
    2 (Cream) Midge
    3 (Gold) Scud
    4 (Gray) Water Strider
    5 (Green) Water Penny Larva
    6 (Ivory) Aquatic worm
    7 (Tan) Beetle Larva
    8 (Orchid) Stonefly Nymph
    9 (Pink) Beetle Larva
    10 (Yellow) Scud

  • Give each student group a copy of the Stream Sampling Classification Sheet and Stream Sampling Worksheet.
  • Be sure students do the sampling in an “eyes-closed” and random fashion.
  • If time allows, have students perform multiple trials in Part II to more accurately estimate the target organism populations.
  • The stream organism sets contain both macroinvertebrates and vertebrates to simulate a more life-like stream sample.
  • The sizes of the organisms used in this activity are not drawn to scale. Use the given sizes as a rough estimate of the actual sizes of the organisms.
  • The organisms from different color sets may be mixed and the numbers and types of organisms may be “stacked” to dramatically sway the water quality values for each student group if desired.
  • The assumption of the mark and recapture technique is that the actual total population is reflected in the same proportion as the trapped population during the recapture. Of course, this technique would only be considered sound with organisms that are easily trapped, tagged, and redistributed evenly back into the original population.
  • With a little research you are likely to find state or local biologists that do random sampling of populations with some regularity. Field trips and/or guest speakers can help to make this simulated laboratory activity take on real-life meaning.
  • This is a great practice activity before conducting an actual study in the field. Research conservation groups in your area to see if such programs are available.

Further Extensions

Alignment with AP Environmental Science Topics and Scoring Components
Topic: The Living World. Ecosystem Structure (Biological populations and communities; ecological niches; interactions among species; keystone species; species diversity and edge effects; major terrestrial and aquatic biomes).
Scoring Component: 3-Living World, Ecosystem Structure.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Asking questions and defining problems
Developing and using models
Analyzing and interpreting data
Using mathematics and computational thinking
Engaging in argument from evidence

Disciplinary Core Ideas

MS-LS2.C: Ecosystem Dynamics, Functioning, and Resilience
MS-LS2.A: Interdependent Relationships in Ecosystems
HS-LS2.A: Interdependent Relationships in Ecosystems
HS-LS2.C: Ecosystem Dynamics, Functioning, and Resilience

Crosscutting Concepts

Cause and effect
Systems and system models
Stability and change

Performance Expectations

HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.

Sample Data


Answers to Questions

Part II.

Target Organism   Water strider   

Number of Target Organisms Originally Captured and Marked    3   

Number of Marked Target Organisms in Second Round Capture    1   

Total Number of Target Organisms in Second Round Capture    3   

T is the number of Target Organisms Originally Captured and Marked
t is the number of Marked Target Organisms Recaptured
n is the Total Number of Target Organisms Recaptured
N is the Population Estimate of Targeted Organisms

Population Estimate of Target Organisms    9   

Actual Number of Counted Target Organisms    10   

  1. Which group level of organisms was most prevalent in your samples?

    Answers will vary. In the sample given, the “other” category was most prevalent.

  2. The following chart can be used as a guide to determine the Biotic Index of Water Quality.

    Use the chart above to determine the overall water quality rating of the two given samples.

    Water Quality

    Sample 1    Poor (Answers will vary.)   

    Sample 2    (Answers will vary.)   

  3. Describe three factors that could affect water quality.

    Dissolved oxygen, temperature, algae growth, pH, pollution, etc.

  4. What steps could be taken to improve the water quality of a body of water?

    Reduce pollution, control algae growth, introduce beneficial organisms.

  5. What factors could affect the overall population estimates found in Part II?

    The number of overall organisms, not enough of the sample organism was sampled, etc.

  6. How close was the calculated estimate of target species to the actual amount counted in step 17? Calculate the percent error using the following equation.
  7. Name an organism (other than the two examples given in the Background section) that the mark-and-recapture technique would work well for. Give an example of an organism that this technique might not work well with. Explain.

    Rabbits, fish, etc. These organisms can easily be captured and released.

Teacher Handouts



EPA–Invertebrates as Biological Indicators, http://www.epa.gov/bioindicators/html/invertebrate.html (accessed June, 2010).

Student Pages

Stream Macroinvertebrate Sampling Simulation


What are those insects and other organisms in the lake or stream? How are the number and variety of these organisms related to the water quality of the lake or stream? Is it polluted? In this activity, a sample of simulated stream organisms will be identified and used to determine the water quality of a simulated natural water source. A widely used population estimation technique will also be performed using these organisms.


  • Water quality values
  • Population size estimation
  • Mark/recapture technique
  • Indicator species


Aquatic macroinvertebrates are found in lakes, streams, ponds and other natural water sources. Macroinvertebrate life cycles go from the egg to adult form and can undergo either complete or incomplete metamorphosis. Complete metamorphosis involves four stages—egg, larvae, pupa and adult. Macroinvertebrates that undergo complete metamorphosis include true beetles, flies and caddisflies. Many of these organisms are aquatic in the egg and larval stages and terrestrial in the adult form. Incomplete metamorphosis has three stages—egg, nymph and adult. Macroinvertebrates that undergo incomplete metamorphosis include mayflies, stoneflies and dragonflies. Many of these organisms, such as dragonflies, also do not live directly in water as adults. Other species such as backswimmers and water striders spend their entire lives in the water. The length of the life cycle of a macroinvertebrate can vary from less than two weeks for some midges to two years or more for some dragonflies and stoneflies.

Macroinvertebrates are commonly used as indicators of water quality because they are sensitive to changes in the ecosystem, spend a large portion (if not all) of their lives in water, and they can be easily collected, analyzed and counted. Macroinvertebrates help maintain the health of water ecosystems by eating bacteria and decaying plants and animals. The quality of a body of water determines what types of organisms can live and survive in that water. Factors that affect water quality include dissolved oxygen levels, temperature, the amount of algae growth, pH and the amount of pollution present. Macroinvertebrates such as mayflies, stoneflies and water pennies need high levels of dissolved oxygen to thrive. Large quantities of these organisms generally are an indication of good water quality.

Other macroinvertebrates, such as leeches and aquatic worms, can survive at lower dissolved oxygen levels because they can come to the surface of the water to obtain oxygen. Low levels of dissolved oxygen are often associated with polluted water while high levels indicate good quality water.

Macroinvertebrate indicator organisms may be grouped into three group levels—Group I, Group II and Group III. Organisms in Group I are very sensitive to pollution and can only survive in very high quality water. Group II organisms are somewhat sensitive but not as sensitive as Group I organisms and can survive in both high and mid-range quality water. Organisms in Group III are tolerant of low quality water and can survive in polluted water. The general quality of water can be determined by the number of different types of macroinvertebrates that are found from each group in a sample. The more types of organisms from the more sensitive groups, the higher the water quality.

A Biotic Index of Water Quality is often used to estimate the quality of a given natural water source. This index is based on the comparison of the types of different macroinvertebrates found from each group level. The higher the Biotic Index the greater the quality of water. In Part I of this activity, two different simulated macroinvertebrate samples will be analyzed and the overall water quality will be estimated using a Biotic Index of Water Quality.

In Part II of this activity, a simulated mark-and-recapture technique will be performed. If a certain species behaves in such a way that it can be easily counted, then accurate monitoring of its population size and density can be easily accomplished. For most species, however, the actual counting of all individuals is not possible. The specific sampling method employed is usually determined by the behavior and habitat of the species in question. Information on mice, for example, may be collected because they are easily trapped. Direct information about wolves, on the other hand, may be hard to secure and might be determined indirectly by collecting their scat.

The key to most population estimates is the use of random sampling procedures. Once random samples are secured, mathematical and statistical techniques are utilized to project the population estimate. Using the mark-and-recapture method, organisms are randomly trapped, tagged and released back into the area where they were trapped. After a period of time, the organisms in that population are trapped once again. The number of animals from the second trapping are divided into two groups, those tagged and those not tagged. The ratio of tagged animals compared to the total trapped population is used to formulate a ratio that is then used to project the total size of the population in the wild. 

Experiment Overview

In this activity, a population of simulated stream organisms will be studied to determine the relative water quality of a given water source. A mark-and-recapture study will also be performed to learn how some populations are estimated in the wild.


Marker, dry-erase
Stream Organism Set, laminated, three different color sets (will be shared with other student groups)
Stream Sampling Classification Sheet
Stream Sampling Worksheet

Safety Precautions

Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines. 


Part I. Water Quality

  1. Obtain a bag containing a collection of stream organisms of the same color from the instructor.
  2. Remove the organisms from the bag and place them face up on the lab table or desktop.
  3. Use the Stream Sampling Classification sheet to classify the types of organisms present.
  4. Write the name of each organism present in the sample in the appropriate group level space on the Stream Sampling Worksheet according to their group level. For example, if a (or several) mayfly nymphs are found, record “mayfly nymph” in the Group I box on the worksheet.
  5. Multiply the number of different types of each organism’s nymph found in each group by the value listed on the Calculation sheet.
  6. Add these three numbers and record the overall Biotic Index Number on the Stream Sampling Worksheet.
  7. Once all data has been recorded, repeat steps 1–6 using another stream organism set.
Part II. Mark and Recapture
  1. Obtain a new, different color set of organisms.
  2. Have a member of the group turn all of the organisms face down on the lab table or desktop without the other members of the group watching.
  3. Obtain the name of the target organism for the specific color set from the instructor.
  4. Have a second group member randomly capture 10 organisms from the tabletop.
  5. Record the number of captured target organisms on the worksheet.
  6. Using a dry-erase marker, place a small X on the front of these captured target organisms.

  7. Without the other members of the group watching, randomly place the 10 captured organisms face down on the table once again mixed in with the remaining organisms.
  8. Have a third group member repeat step 11. Record the total marked and unmarked target organisms captured on the worksheet.

  9. Use the equations on the worksheet to estimate the total number of target organisms in the given population.
  10. After the estimated number of target organisms has been calculated, turn all of the organisms face up and count the actual number of target organisms in the total population. Record this value in the worksheet.
  11. Erase the marks from the organisms and answer the Post-Lab Questions.

Student Worksheet PDF


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