FOCUS: Water in a stream rushes, splashes, tumbles, or flows smoothly, creating different conditions and homes for a variety of organisms. In spite of the challenges of life in moving water, the streambed teams with insects. Many feed on plant and animal debris, helping to break down organic material that falls into the water, and they in turn provide a rich source of food for fish, birds, salamanders, and other stream inhabitants.
INTRODUCTION
Objective: To begin to explore and ask questions about stream life.
Standing near a stream, take a minute to stop, listen, and look. Ask children what they notice and wonder about the stream and what animals might live in it.
STREAM SAFARI
Objective: To look for evidence of insects or other small creatures living underwater in a stream.
Ask the children how we could find out what kinds of stream creatures live in our stream. We could look for them in the places where they normally live underwater in a stream, noticing how many different kinds we find. Three good ways to do this are: 1) pick up rocks and look for insects, snails, or their cases stuck to them; 2) cast nets for floating insects; 3) gently move the rocks, leaves, and gravel on the stream bottom, and use nets to catch anything that floats out from under them.
Beside the stream, place several white basins containing a few inches of clear stream water near where students will be working (on the bank or on a beach area). Demonstrate ways to collect stream creatures, emphasizing the need to treat them with great care:
- Lift small rocks out of the water. Turn them over and look for creatures clinging to the rocks. Gently lift creatures off the rocks and place them in the basins to observe.
- Use a net to dip into eddies and pools and gently probe vegetation in the water. Lift critters from the net and place them in basins.
- Place the net on the stream bottom and hold the handle upright. Stand upstream of the net and use hands or feet to move sand, gravel, or stones around so that the water washes things out from under them and into the net. Then look for wiggling insects in the net. Lift them out carefully with a spoon or with your fingers and place them in basins, being careful not to add debris to the basins which makes it hard to see the critters.
Give children plenty of time to observe insects in the basins, noticing their appearance and behavior. For closer observation, put insects into small jars or other small white containers. Use magnifying lenses to examine specimens. Use the Aquatic Insect Search card to look for differences in appearance and behavior. Or, using the Pond and Stream Critter guide, try to match critters to the pictures, if possible. About how many different kinds were found in all? Do some seem to be different sizes of the same insect? Which kinds were the most common and which were the rarest?
Materials: white plastic basins, nets, plastic spoons, small clear jars or white containers like yogurt cups, magnifying lenses, Pond and Stream Critter guide and/or Aquatic Insect Search card; optional: wading boots, Quick Reference Guide to Aquatic Invertebrates.
UPPER GRADES CHALLENGE: Critter Clues to Stream Health (Grades 5-6)
Objective: To evaluate the health of a stream based on the kinds of macroinvertebrates that are found living in its waters.
With the live specimens collected in the Stream Safari above, help students make a tally of the numbers and kinds present. You will need to be able to recognize mayflies, stoneflies, and caddisflies, but all others will just need to be counted, not identified. Explain that mayflies, stoneflies, and caddisflies are highly sensitive to pollution in the stream. The proportion of these insects in a sample gives a rough estimate of stream health. This is called the Percent EPT index.
EPT is short for Ephemeroptera (mayflies), Plecoptera (stoneflies) and Tricoptera (caddisflies).
To calculate the Percent EPT:
- Count the total number of mayflies, stoneflies and caddisflies collected (= EPT).
- Count (or estimate) the total number of all macroinvertebrates collected (= Total).
- Divide the EPT by the Total and multiply by 100 to get a percentage (= Percent EPT).
- The higher the Percent EPT, the cleaner the water, since these organisms cannot tolerate pollution: 50% or greater is good; 25% to 50% is moderate; less than 25% is poor.
Ask questions to prompt a discussion of these results such as:
What can you say about the conditions in this stream from the results?
If possible compare your results with those from another class. How similar or different are they?
How well do you think this sample represented all the insects in the stream? Could they have missed some kinds, or inadvertently collected the larger, more active kinds? What could you do differently to control for these problems?
Afterward, have the students carefully return the animals to the stream near where they were collected.
Materials: insect collections from Stream Safari; for each team: Pond and Stream Critter guide, paper, pencils, clipboards, plastic spoons and small containers to aid in counting and sorting animals; optional: calculator, Quick Reference to Invertebrates.
STREAM MEASUREMENTS
Objective: To look for evidence that stream speed and temperature vary along its course.
Water Speed
Find a place along the stream bank where it is possible to measure off a ten-foot distance with a measuring tape or 10′ length of rope. Place a marker at each end. Assign one child to be time-keeper and one to be the thrower. At the leader’s signal, the thrower tosses a stick or other biodegradable item that floats (pinecone, apple, etc.) into the water, a little upstream from the starting marker. Begin timing when the stick floats by the “start” marker and end when it passes the “finish” marker. Use a net to catch the object. Repeat several times and average the results. Stream speed is measured in feet per second. Calculate the speed from your results:
Number of seconds it took to go ten feet _______
Distance (ten feet) divided by time (number of seconds) = feet per second______
Compare measurements of stream speed with other groups. Would the speed be the same everywhere in the stream? Where might it be faster? Slower? Ask the children to consider how this could be tested. (Measure the speed in different sections of the stream for comparison.)
Do you think this is a deep pool with slow-moving water, a run with smooth, fast-moving water, or a riffle with shallow, choppy water and a rocky bottom? Why is fast-moving water better for stream insects? (Faster water holds more oxygen.)
Water Temperature
Place a thermometer in the shade to measure the air temperature. Place the stream thermometer in the water and wait at least three minutes to read the temperature. How does the stream temperature compare to the air temperature? Compare temperature with other groups at different locations. Was stream temperature the same throughout? What might account for differences? (Shade or lack of shade, depth of water, etc.) Why is colder water better for stream insects? (It holds more oxygen than warm water.)
Materials: for each group: measuring tape or 10′ length of rope, timer; biodegradable floating object such as a stick, pinecone, apple; net for catching object, stream thermometer on a rope, clipboard, pencil, Stream Measurements sheet; optional: wading boots, calculator.
STREAM CRITTER FAREWELL
Objective: To carefully return animals to the stream.
Ask the children to bring their insect specimen in its jar to a gathering place by the edge of the stream. Remind them that these small creatures can only survive in the stream. Have them repeat each line of the goodbye poem after you, before releasing their animals.
Goodbye Poem
I looked at you,
You looked at me,
I’m glad we met,
And now you’re free.
Goodbye!
Now instruct children to carefully return the animals to the stream and watch them swim away.
Materials: copy of Goodbye Poem, laminated or in a plastic sleeve.
PUPPET SHOW “The Net Result”
Objective: To learn about some insects that live in streams and their roles in the food web.
Perform the puppet show, or have a group of children perform it for the class. Afterward, ask questions to review the key details and vocabulary in the story, including the different insects and their roles in the stream food web. How did the mayfly keep from being swept away? (Hooks on feet.) How did the stonefly get oxygen? (Gills under its legs.) How did the caddisfly keep safe and secure on its rock? (Builds a case attached with glue.) Why do these insects prefer places with fast-moving water? (It has more oxygen in it.) Which character was an algae scraper (mayfly), a shredder (stonefly), a collector (caddisfly)? How are shredders important to collectors? (They shred leaves into smaller bits that collectors can eat.) What might like to eat these insects? (Salamanders, fish, frogs, birds, other insects.) Why do these insects have the word “fly” in their names if they can’t fly? (They are in immature stages; after metamorphosis they will become flying insects.)
Materials: puppets, script, stage, props.
JOURNAL ACTIVITY: Streamside Sketching
Objective: To notice and record in drawings the features of a nearby stream.
Bring children to visit a nearby stream. Supply children with paper, pencils, and clipboards. If possible, take small groups of children with an adult to different places along the stream. To begin, ask children specific questions and prompt them to point out features they can see.
Is it shaded or sunny?
Is it steep, sloping, or flat?
Is it straight or curving?
Are there places where the water is smooth? Choppy?
Are there any waterfalls?
Are there boulders, rocks, gravel, or sand in the streambed or on the banks?
Are there plants in the water? Where?
Are there trees on the banks? Other plants?
Ask the children to include as many of these details as they can in their drawings. If practical, let children color in their drawings, or paint them with watercolors and stream water. Include stream creatures in the places where they were found. In small groups, have the children share their sketches or paintings.
Materials: journals or clipboards and paper, pencils; optional: crayons or watercolor paints and paintbrushes, small dishes of stream water.
CLOSING THOUGHTS
Objective: To review what has been learned by studying the stream.
Have children complete the sentence: “My favorite stream critter we found today was _______ because__________ .”
A STEP BEYOND
Catch and Release: If it’s not possible to get to a stream with the children, collect some stream water and stream creatures in clean buckets and bring them to a place where children can observe them. Gently pour the water and critters into white basins, keeping them in the shade and spacing them apart so children can gather around. Look for differences in appearance and behavior. Afterward, carefully return the critters to the stream where they were collected.
Nearby Nature 