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Macroinvertebrates as Indicators of Pollution

Abstract

In this science project, you will collect macroinvertebrate samples from multiple points along a body of water, ideally a small creek or stream, and test the pollution burden and biodiversity of small organisms or insects to see if pollution impacts biodiversity.

Summary

Areas of Science
Environmental Science
Difficulty
Method
Scientific Method
Time Required
Short (2-5 days)
Prerequisites

None

Material Availability

Readily available

Cost
Very Low (under $20)
Safety

Ensure it is permissible and safe to take water samples in the creek you plan to sample. Some contaminants in waterways may be unsafe. Take proper safety precautions, including wearing waterproof boots or gloves, and not working in unsafe conditions.

Credits
Laura Ohl, PhD, Science Buddies Alumni

Inspired by research by Dr. Santiago-Blay of Penn State, York campus.

Science Buddies is committed to creating content authored by scientists and educators. Learn more about our process and how we use AI.
https://www.youtube.com/watch?v=tUaA7Q7GSII

Objective

Students will collect trash and macroinvertebrates and then assess the population size of each species and their susceptibility to pollution to better understand how pollution impacts a creek's biodiversity. 

Introduction

The increase in natural disasters and pollution has drastically decreased the population sizes of biological organisms globally. Why is that problematic for our planet? Biodiversity is known as the diversity of life on earth that helps build a healthy ecosystem, allowing for clean air, pure water, and nutrient-rich soils for food production. Therefore, less biodiversity is an indicator of an unhealthy habitat, which will impact every organism in that environment, including humans. But what causes loss of biodiversity? Habitat destruction is one of the leading causes of biodiversity loss, which is known as the decrease in the genetic biodiversity or variation within a species in that area. Biodiversity loss typically results in the eventual extinction of a species. More and more species are becoming extinct every day due to environmental changes. 

So, how can we assess biodiversity to understand if an ecosystem needs our help? One fun way is to assess the biodiversity of macroinvertebrates, also known as large invertebrates. Aquatic macroinvertebrates are organisms found in waterways and are often easier to see and observe in small creeks. In these small waterways, dragonflies, caddisflies, stoneflies, beetles, midges, and mayflies are found, although these macroinvertebrates may be harder to find or catch. In Lancaster, Pennsylvania, the presence of hatching mayflies over parts of the creek and even on the overcrossing bridges is a sign of improved water quality of the river, since these macroinvertebrates are intolerant to pollution. Ecologists use this knowledge to understand if a waterway has good water quality and is safe for biodiverse organisms, and determine which ones.

How do ecologists use macroinvertebrates to assess the quality of water? They survey the organisms in the creek beds (center) and creek banks (edges) to better understand what pollution-resistant and unresistant organisms are there. In this science project, you will identify the species in your local creek and quantify the population size of each species. You will then use the information, along with observations of the creek, to determine if the creek is polluted without requiring expensive equipment. Then you can be a community ecologist and recognize polluted waterways in the future to inform your community if waterways are polluted and need to be improved. 

Image of labelled creek. Image Credit: Laura Ohl, PhD / Science Buddies

Image of labelled creek ecosystem showing location of creek bed in the center of the creek and creek banks on the edges.

Figure 1. Image of labelled waterway ecosystem showing creek bed and banks. 

Terms and Concepts

Questions

Bibliography

Materials and Equipment

Experimental Procedure

Download PDF of Procedure
This project follows the Scientific Method. Review the steps before you begin.

Experimental Background

Do some background research on local watersheds to determine the best locations to study macroinvertebrates in stony bottom creeks. If there is a non-public water source, ask for and obtain permission to collect water samples from it. Additionally, be prepared to go into the creek bed to collect macroinvertebrate samples by bringing waterproof shoes, such as rain boots. 

Observing Creek Pollution and Macroinvertebrate Populations

  1. Locate a stony bottom creek and a riffle, or fast-flowing areas of the creek that run over rocks, as seen in Figure 2.
  2. Get proper permission from your local water authority to take samples from the creek. This will ensure your safety and the long-term safety of the creek's aquatic organisms.
  3. Choose an area to collect the macroinvertebrates from using the rock method by turning over rocks where macroinvertebrates live in higher concentrations. Choose rocks from the riffles, or fast-flowing areas of a creek that have ripples or small waves. Generally, the longer the stretch of riffles, the more likely to find invertebrate life, although you can find some in slower areas, too. We recommend that the area have a stretch of riffles or waves of at least 10 meters long.
  4. Before you collect your samples, ensure you have waterproof shoes on to protect yourself from potentially polluted water.
  5. Put your gloves on.
  6. Observe the creek area for common waste pollution. Count the number of unique trash items and the quantity of each group of items, then record the results in Table 1. 
  7. Fill your collection container and sorting containers with creek water.
  8. One at a time, collect 5 rocks that are at least 4 cm in width or more from the upstream end, within the riffle. 
    1. Carefully go to the middle of the creek and pick up a rock submerged under water.
    2. Slowly flip it over to reveal any macroinvertebrates and to prevent them from falling off the rock.
  9. Gently remove the invertebrates from the rocks or stones, being careful not to squeeze too hard with the forceps to keep the macroinvertebrates alive. 
    1. Transfer the stone to your tray filled with creek water.
    2. Using your forceps, gently remove any visible macroinvertebrates and transfer them to the sorting tray filled with creek water to sort them, as seen in Figure 3. 
    3. Repeat these steps for 5 rocks at the first spot at the upstream end, within the riffle.
  10. Group or classify the number of invertebrates from the creek.
    1. Move macroinvertebrates into matching body shapes or species, if not already. 
    2. Take a picture of each type of invertebrate, and use a macroinvertebrate field identification guide, a macroinvertebrate key card, or AI tools such as google lens to identify each group of unique invertebrates. 
    3. Count the number of each invertebrate, and record your observations in Table 1.
  11. Repeat this process for the downstream end within the riffle, collecting samples from a total of 10 rocks from the area. 
  12. When done identifying, counting, and classifying the invertebrates, return them to the creek. 
  13. Clean all equipment thoroughly, particularly if you plan to use it at another location with water. This will prevent the spread of invasive species and pollutants.  
  14. Review your data to draw conclusions about whether the waterway is polluted and to what extent it impacts the biodiversity of the creek. 
    1. Based on your pollution observations, is the creek safe for recreational use (swimming, fishing)?
    2. What macroinvertebrates were most abundant or common based on your observations? Does this compare to previous historical research on the creek?
    3. Were there any pollution-susceptible macroinvertebrates present in your creek samples? What does this tell you about how polluted the creek may be?
    4. Are there any limitations to this method of collecting representative macroinvertebrate samples from other areas of the creek ecosystem? 
Image of riffles.Image Credit: Laura Ohl, PhD / Science Buddies

Image locating riffle in creek.

Figure 2. Image of creek riffles, where macroinvertebrates are commonly found.
Image of sorted macroinvertebrates.Image Credit: Laura Ohl, PhD / Science Buddies

Image of sorted macroinvertebrates in a sorting container.

Figure 3. Example of sorted macroinvertebrates in a sorting tray.

Swipe left to see more
Table 1. Signs of pollution and its relationship to macroinvertebrate populations. 

Creek name and number of rocks sampled:

Number of pieces of trash collected:
Name of each unique macroinvertebrate  Number of each invertebrate (population size) Relative abundance (rare, common, abundant)  Susceptibility of macroinvertebrates to pollution 

Macroinvertebrate 1 :

Macroinvertebrate 2 : 
....



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Global Goals

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.

This project explores topics key to Clean Water and Sanitation: Ensure access to water and sanitation for all.
This project explores topics key to Life Below Water: Conserve and sustainably use the oceans, seas and marine resources.

Variations

  • Take samples from multiple locations throughout the creek, such as the center or sides. Additionally, you can see if there are different species in different current speeds or water depths. Explore this question to understand how different areas of a creek may be more or less impacted by microenvironments and their relationship to common indicators of pollution in creeks.
  • Not all pollution is easily visible by eye! What about non-obvious or invisible signs of pollution? Asses how polluted the creek is with aquatic chemistry methods like using a test kit for common pollutants. Do these tests correlate better with the macroinvertebrate population sizes?
  • Classify the macroinvertebrates by niche, or ecosystem groupings like consumers, predators, and decomposers. What does this tell you about the overall health of the creek, and what may be missing from the ecosystem? 
  • Compare the populations of macroinvertebrates at multiple locations along a creek. How do the signs of pollution impact the biodiversity of organisms throughout the creek? 
  • Use other methods of creek sampling, such as scoop nets and kick nets. Do these methods collect different types of macrovertebrates? Are any of these methods more effective at assessing the overall pollution susceptibility of macroinvertebrates in the creek? Compare the samples collected for each method to assess this.
  • Observe the creek for signs of excess nutrients or erosion along the creek bank, as an indicator of pollution. Create a scoring system to help quantify the results, with the creek banks having 2=covered, 1=half covered, and 0=none. Does this pollution indicator correlate with the amount of creek pollution or the quantity of pollution-susceptible organisms in the creek? 
  • After you assess the biodiversity of your local creek, do some research on how you can improve its biodiversity by remediating the environment. Some ideas could include adding plants to the creek's edge to prevent erosion or finding ways to safely remove pollutants from the waterway. Work with your local environmental center to see if you can implement this change and see the results before and after your intervention.

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Cite This Page

General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Ohl, Laura. "Macroinvertebrates as Indicators of Pollution." Science Buddies, 10 July 2025, https://www.sciencebuddies.org/science-fair-projects/project-ideas/EnvSci_p078/environmental-science/Water-Pollution-and-Biodiversity. Accessed 23 June 2026.

APA Style

Ohl, L. (2025, July 10). Macroinvertebrates as Indicators of Pollution. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/EnvSci_p078/environmental-science/Water-Pollution-and-Biodiversity


Last edit date: 2025-07-10

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