Why is the pond green?

Students investigate the phenomenon of an algal bloom on an Illinois pond. They compare and contrast pictures of the pond, one in the spring when no algal bloom is present, and one in the late summer in which the surface is green. The students share their related experiences, ask questions about the pond to develop a Driving Question Board (DQB), and determine ideas for investigations. Their questions drive the flow of the unit. Students plan and carry out own investigations to answer these questions, which includes growing algae in a variety of conditions. Students examine data and maps to ultimately inform the development of a community action plan to prevent algal blooms.

About This Unit

This surface water unit has been created by the Office for Mathematics, Science, and Technology Education (MSTE) in collaboration with the Illinois Environmental Protection Agency (EPA). This unit is aligned to the Next Generation Science Standards (NGSS) to provide ease in supplementing environmental education in the formal classroom but is also suitable for informal use. It has been designed to develop critical thinking skills, and to encourage students to think constructively about environmental issues and to make informed decisions about our natural resources.

Pathway Overview

The Pathway Overview shows the conceptual and coherent flow of the entire unit.

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ask Ask
observe Discover
image/svg+xml Learn
How does the pond change?
Sometimes the pond is covered with green stuff.
What is the green stuff?
It's green and looks like a plant.
Is it a plant?
The green stuff is called algae and it needs air and light to grow.
Where did the algae come from?
Algae is already in the water and can grow from regular tap water.
Why is there so much algae in the summer?
Days are longer and warmer in the summer. It is also the time of the year when people use fertilizers on their lawns and farms.
Does algae grow more with fertilizers/extra nutrients?
Algae grows rapidly when there are extra nutrients in the water.
Where did the extra nutrients come from?
Our pond is at the lowest elevation in the area. Any fertilizers used on lawns or the farm would run right into the pond when it rains.
What else is in the pond?
There are many living things that live in our pond ecosystem like fish, insects, turtles, birds, and other plants.
Is our pond ecosystem balanced?
We do not think that our pond ecosystem is balanced in the summer. Less sunlight reaches the plants at the bottom of the pond when there is an algal bloom. This affects the other plants and animals in the pond.
Where else does this happen?
Algal blooms happen in many areas in the United States. The Gulf of Mexico Dead Zone is caused by excess nutrients being transported by the Mississippi River. As algae grows unchecked, the food chain changes, and the oxygen in the water gets used up, making it difficult for anything to grow there.
How can we prevent algal blooms from happening?
We developed a community action plan to keep our ponds as healthy as possible during the summer months.

Teacher Guide

This document details the flow of lessons from the teacher perspective, including lab set-up and safety instructions, suggestions for discussion prompts, and examples of student work to assist in planning. Individual lessons from the Pathway document are included for reference, followed by detailed learning plans.

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Material & Supply List

A number of consumable and non-consumable materials and supplies are used during investigations. Some additional, optional equipment can enhance the investigations if available.

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Student Activity Sheets

Lessons in the Teacher Guide reference specific activity sheets; you can find links to these sheets below. By making a personal copy of an activity sheet in Google Drive, you can modify it to suit your particular classroom's needs.

  • Anchoring Activity: Used in Lesson 1 to help students organize their observations and questions about the anchoring phenomenon, a green pond.
  • Investigation 1: Can We Grow It?: Used in Lesson 4 to design an investigation on algae's ideal growing conditions.
  • Activity 2: Community Pollution: Used in Lesson 7 to explore how community pollution might contribute to algae growth.
  • Final Models: A final assessment used to synthesize information learned throughout the unit into a working model of algae blooms.

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Readings & Maps

Lessons in the pathway make use of additional materials such short readings and maps. 

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All Materials

You can find all of the materials listed above and more in our public Google Drive folder. These documents can be downloaded or copied into a private Google Drive and modified for classroom use.

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Unit Resources

Interested in learning more about algae, surface water, and ecosystems? Looking for additional lessons and activities for other grade levels? The resources below take you to online simulations, related curriculum developed by others, factsheets about algae and surface water, and more!

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Illinois EPA University of Illinois at Urbana-Champaign

These materials were developed with support from an Intergovernmental Agreement from the Illinois Environmental Protection Agency under agreement number IEPA 18-01 awarded to the Office for Mathematics, Science, and Technology Education in the College of Education at the University of Illinois Urbana-Champaign. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Illinois Environmental Protection Agency.