Classroom activity Grade 6 Science
The Otter Run Stream Survey: A Water Quality Bug Hunt
A grade 6 science station activity where students sort stream-bug cards from three sites and rate each site's water quality using sensitive and tolerant bugs.
Objectives
- Students will sort stream bugs into sensitive, somewhat sensitive, and tolerant groups using an identification key.
- Students will rate each site's water quality from which bugs are present.
- Students will infer how runoff from land affects the bugs living in a stream.
Vocabulary
- Dissolved oxygen
- Dissolved oxygen is the oxygen gas mixed into water that fish and other underwater animals breathe. Cold, moving water holds more oxygen than warm, still water.
Also: macroinvertebrate, bioindicator, sensitive species, tolerant species
Teacher overview
Otter Run is a fictional stream that scientists check for health by looking at its bugs. The small animals that live under stream rocks, called macroinvertebrates, are bioindicators: some kinds need clean, high-oxygen water, while others can live in dirty water. Most fish need dissolved oxygen above 5 mg/L, and the same clean water that fish need is where the sensitive bugs live. In this station activity, groups of 3 or 4 students "collect" bug cards from three sites along Otter Run, sort them, and rate each site's water quality. The activity works because the cards at each site match the bugs that would really live in water of that quality.
Activity Directions
- Before class, set up three stations. At each station, place the sign and the matching bug-card set. Site A is upstream in a forest. Site B is downstream, just below a large parking lot. Site C is downstream, just below a farm field. The card sets are:
- Site A cards: mayfly nymph, stonefly nymph, caddisfly larva, water penny, riffle beetle, gilled snail.
- Site B cards: dragonfly nymph, damselfly nymph, aquatic worm, midge larva, leech.
- Site C cards: caddisfly larva, crayfish, scud, midge larva, pouch snail.
- Open by explaining that sensitive bugs need clean water with lots of oxygen, tolerant bugs can live in dirty water with little oxygen, and somewhat sensitive bugs are in between. Show the identification key so students can see which group each bug belongs to.
- Hand out the recording sheet and the identification key to each group. Assign each group to a starting station.
- At each station, the group "collects" the sample by turning over the site's cards. They use the key to sort the bugs into three piles: sensitive, somewhat sensitive, and tolerant.
- The group counts how many different sensitive kinds they found and rates the site: 3 or more sensitive kinds is Good, 1 or 2 is Fair, and none is Poor. They write the rating on their recording sheet.
- After about 9 minutes, groups rotate to the next station. Repeat until every group has visited all three sites.
- Bring the class together. Have groups report their rating for each site and fill in the class chart on the board.
- Debrief with the recording-sheet questions, focusing on why Site A scored higher than Sites B and C, and what the land above each site has to do with the result.
Student Handout
Bug identification key:
- Sensitive kinds (need clean water): mayfly nymph, stonefly nymph, caddisfly larva, water penny, riffle beetle, gilled snail.
- Somewhat sensitive kinds: dragonfly nymph, damselfly nymph, crayfish, scud.
- Tolerant kinds (live in dirty water): aquatic worm, midge larva, leech, pouch snail.
Rating rule: 3 or more different sensitive kinds is Good, 1 or 2 is Fair, and none is Poor.
Record your work and answer these questions:
- List the bugs you found at each site, sorted into the three groups. What rating did you give each site?
- Which site had the most sensitive kinds, and which had the fewest?
- Site B is below a parking lot and Site C is below a farm field. Explain how runoff from those places could change which bugs live there.
- Otter Run's water looks clear at all three sites. Explain why the bugs can tell you something about water quality that just looking at the water cannot.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
Site A should be rated Good, with sensitive kinds such as mayfly, stonefly, caddisfly, water penny, riffle beetle, and gilled snail. Site B should be rated Poor, with only tolerant and somewhat sensitive kinds such as dragonfly, damselfly, aquatic worm, midge, and leech. Site C should be rated Fair, with one sensitive kind (caddisfly) plus crayfish, scud, midge, and pouch snail.
Site A had the most sensitive kinds and Site B had the fewest (none). Accept answers that match the student's own sorted cards and the rating rule.
Rain washes oil and salt off the parking lot and fertilizer off the farm field into the stream. That runoff can lower the oxygen and add pollution, so sensitive bugs die out and only tolerant bugs remain. Accept any answer connecting runoff to worse water and fewer sensitive bugs.
The bugs live in the water all the time, so they show the water's health over weeks, not just the moment you look. Clear-looking water can still have low oxygen or pollution, which the missing sensitive bugs reveal. Accept any answer with this idea.
Differentiation
Support
Give students bug cards with the group name printed on the back so sorting is a check rather than a guess. Pair students who need help with a peer, and provide a partly filled recording sheet where Site A is already sorted as a worked example.
Extension
Ask students to design a follow-up plan: where along Otter Run they would add a fourth sampling site to test whether the farm or the parking lot causes more harm, and what bug result would point to each source. Have them predict the ratings.
ELL supports
Provide picture cards of each bug with its name and group, and a color code for the three groups (for example, green for sensitive, yellow for somewhat sensitive, red for tolerant). Allow students to answer the debrief questions with labeled drawings or short phrases.