For this activity, access to a stream, creek or pond is required. There are two options of obtaining samples for this activity: as a class, walk to a stream to collect a sample or have just one adult get the stream sample in advance. (Note: A 1-liter sample of stream, creek, or pond water for each student group should be acquired). The water samples are best if a rock, covered in dirt and debris, or a slimy stick from the stream bottom is included in each.

This activity is written with the assumption that students will walk to a stream, but it can easily be used for already-prepared samples.

Print out (and consider laminating) the three Macroinvertebrate Identification Sheets - Groups 1, 2 and 3 (see Attachments) for students to share to identify their water life.

1. Ask the students the following question: "How can we determine if a stream is healthy or not?" Tell them that this is the question they are going to answer today. There are many possible answers, and we are going to explore some methods used by engineers to help us come up with a solution.
2. Divide students into groups of 4. Each group should take a water sample (about a half liter) from the stream in a jar or tub. Try to include at least one rock —covered with dirt and debris — in each sample.
3. Ask students to use the thermometer to determine the temperature of the water sample and record on their Stream Consciousness Worksheet.
4. Then, they should use the pH tester or pH paper to determine the pH of the water and record on their Stream Consciousness Worksheet.
5. Have students record on the activity sheet any other observations or physical characteristics of the water (odor, color, what things are floating or sinking in your sample).
6. Next, ask students to pour a small amount of their water sample onto a petri dish or tray for observation. Using the macroinvertebrate identification chart and a dissecting microscope or magnifying glass, they should identify as many macroinvertebrates in the sample as possible. Have them list on the Stream Consciousness Worksheet which invertebrates and how many of each are found.
7. Student should then take another small amount of their sample and continue counting and identifying macroinvertebrates until they have examined the entire sample. Note: students do not need to count more than 150 invertebrates.
8. Have students count how many of each different kind of macroinvertebrate are found in their sample and write down whether they think their sample indicates good, medium or bad water quality and why.
9. Have the students create their own "rating scale" to determine the biotic index of the water. Example: for "good" invertebrates, assign a value of 10 point to each. For "bad" invertebrates, assign a value of 2 point to each. They should total the points for "good" and "bad" invertebrates and divide by the total number of invertebrates (average bug value). Have them compare this to your (teacher's) rating scale to determine if the stream is good or bad water quality.
10. Compare your analysis with the class. Did each group come to the same conclusion? Why or why not?
11. Have each group report to the class the number of macroinvertebrates and how they rated the stream. Record the numbers on the board. As a class, calculate an average number of macroinvertebrates found and discuss any discrepancies in rating the stream. Did all the students find that it was very healthy? Or did some students rate the stream poorly while others found it was clean?
12. Ask the students to define why they rated their sample as they did.
13. Review with the students why engineers would care about water quality. Discuss how changes in water quality affect drinking water, or how water quality is used as an indicator of harmful industrial discharges or fertilizer use. Discuss how engineers may be involved in stream maintenance or restoration.

Brainstorming: Ask students what they think are indicators of water quality. As a class, have the students engage in open discussion. Remind students that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Have them raise their hands to respond. Write their ideas on the board. (Answers may include some of the following: smell, color, murkiness, number of macroinvertiberates, pH, and presence of trash.)

Hypothesize: Have students hypothesize whether or not they think the stream or sample they are going to investigate is healthy. Why or why not?

Worksheet: Have the students record their measurements and observations and follow along with the activity on the Stream Consciousness Worksheet. After students have finished their worksheet, have them compare answers with their peers.

Rate It!: Have the students create their own rating scale to determine the biotic index of the water. They should assign numbers to good and bad water quality macroinvertebrates and develop a way to quantify the health of the stream sample.

Take a Stand!: Have students write a persuasive essay (teacher should set length depending on time available to spend on writing). In the essay, students should pretend they are environmental engineers that were asked by the community to evaluate a stream. Their essays should clearly explain how they rated the stream and why.

• Alternatively, each group of students can create a PowerPoint® presentation and make a presentation to the class. In this case, the class would role play a group of experts from the community, including business leaders, citizens and other engineers.