Objective: By completing this activity the students should be able to: Identify the steps
and process involved in lake and river monitoring, Understand why algae and other
aquatic plants grow in water and determine what levels of turbidity are healthy for a lake,
and understand the effects of sedimentation on a water body.
Materials: 1/2 teaspoon of instant iced tea mix, 1/2 teaspoon of sediment, water, Cool,
Clear Water activity map, plastic spoons, EPA's "Citizen Lake Monitoring Program"
video, 3 - 60 cm turbidity tubes, pitcher
Background: Lakes are much more than for groundwater, surface water, and
precipitation to collect. They also control flooding, provide habitat for fish and wildlife
and give us places to swim, boat, and fish. In addition, many people value lakes for their
Each lake is unique in appearance, chemistry, biology, and physical characteristics.
Even within lakes, these attributes can vary. For instance, water at the surface of deep
lakes may be chemically and biologically different than water at the bottom. In shallow
lakes, the differences between top and bottom waters are less.
Moderately deep lakes undergo a natural aging process known as eutrophication. They
gradually fill in, becoming ponds, marshes, wetlands, and eventually, forests.
Depending on the trophic state (or how biologically productive), lakes can be clear,
nutrient-poor and with little life (oligotrophic); murky, nutrient-rich and full of life
(eutrophic); or somewhere in between (mesotrophic). How a lake functions and ages is
determined in part by its size and volume, how much sunlight it receives, the length of its
shoreline and the health of its watershed.
We all want lakes to be healthy, with clean water, good recreational possibilities, plenty
of fish and wildlife and no pesky insects or weeds. However, our everyday actions can
profoundly affect these fragile aquatic ecosystems, degrading the very qualities that
attracted us to them in the first place. For example, nutrients in fertilizers, detergents,
failing septic systems, eroding soil, and animal waste can cause algae to bloom and
aquatic plants to grow and multiply rapidly. Algal blooms can greatly reduce water
quality, and too many aquatic plants can clog lakes, interfering with swimming, boating,
and other recreational uses. There are many other ways we can affect lakes. By
removing dirt and native plants from a shoreline, we can unintentionally encourage
erosion or allow non-native plants to take over.
Realistically, few lakes can satisfy all our individual desires. At best, we can strive for a
balance - to keep each lake healthy and serve our needs too. There are many ways that
people can help lakes that include joining a local lake association protecting the lake by
controlling runoff (minimizing the use of fertilizers, using environmentally friendly garden
products and using native plants as buffers around shorelines), becoming a "healthy
lake" advocate, and becoming a volunteer lake monitor (people or groups who caretake
for the lake by water sampling, planting native plants and monitoring turbidity
Turbidity is the measure of water clarity or how much light can pass through water.
Water clarity is reduced (and turbidity is increased) when there is too much material,
such a soil particles, algae, plankton, microbes and other substances, in the water.
Excessive turbidity over a period of time can negatively affect fish and other aquatic life
by raising the temperature of the water, reducing photosynthesis or aquatic plants, which
in turn reduces the amount of oxygen available for fish and clogging fish gills.
Lakes and streams all have a level of turbidity that should be monitored to ascertain the
health of the water body. Turbidity can be measured by lowering a secchi disk into the
water body and immersing it until it's no longer visible. You then measure the depth at
which it disappeared; this will determine the amount of turbidity in that water body, thus
supplying the information needed to help determine the health of the lake or stream.
The greater amount of turbidity, the less likely it is that the lake/stream and its inhabitants
Referring to the map, ask the class to identify the lakes and streams. Briefly discuss
why lakes are important to the state. Lead a discussion about how water is replenished
in lakes (by streams, rain and groundwater).
Show the video. Have a follow-up discussion about what type of citizen involvement was
shown, how they, as a class, could participate in this type of program and what they
learned about lake clarity as an indication of water quality in a lake. Divide the class into
3 groups. Assign a group to each column. Make sure the drain tubes are closed by
squeezing the crimp. Have each group pour water into their column from the faucet,
filling the tubes around 3/4 full.
Column 1 is clean water. Have group one view the secchi disk located at the bottom of
the tube. It should be visible all the way to the bottom. Ask for comments about the
health of such a lake (possibly nutrient-poor water - lake may not be in very good
shape!). Explain the circumstances to the class of the lake with clear water. Responses
to all the questions and discussions will vary.
Column 2 is water with the soil (sediment). Add 1/2 teaspoon (or a little less) to the tube
after it's been filled with water. Place your hand over the opening at the top and gently
stir the water/sediment mixture. Talk briefly about how sediment can enter a lake
(through runoff and by other means). Have a few students measure the clarity of the
water looking into the tube and slowly draining the tube, using the hose crimp to slowly
allow water to drain out of the drain tube (when students can read the secchi disk, stop
draining the water. Have the group take a measurement). Water clarity will not be as
good as Column 1, but visibility should be fairly good. Discuss with the class what
happens to the lake by additional water entering it, recreational use (boats, jet skis, and
others), wildlife, etc. Allow the sediment to settle back to the bottom. After the sediment
has settled, place your hand over the opening and again gently agitate the sediment in
the column. Have the students re-measure the water clarity now. What is the difference
in their measurements? Ask for comments about the health of such a lake.
Column 3 is water with iced tea mix. This column is a representation of algae or other
biological material that can grow in lakes that receive too many nutrients (an example to
use is lake land owners over-fertilizing their lawns thus causing fertilizer to runoff and
enter the lake). Add 1/2 teaspoon of tea mix to the column. The tea mix should be dark
enough so that the disk is no longer visible at the bottom of the column. Follow the
same procedure as with Column 2, draining water until the secchi disk is visible. After
measuring, point out how the material in Column 3 does not "settle out" in the lake as it
does in Column 2.
Ask the students to identify the ways water could have ended up as it is in each column
(if it were a real lake). Lead a discussion with the class on options of getting involved
with a local lake monitoring program.
Note: this activity can be conducted at a lake. In that case, additives may not be
necessary. A suggestion would be to have each group of students take a water sample
at different location on the lake and then compare water quality from each site.
Introduce the phrase, "Think globally, act locally". Apply the concept to a discussion of
tributaries and lakes. Discuss possible local streams or lakes that your class could
adopt. Explore possibilities of involving local agencies, groups and/or organizations
such as a local lake/citizens monitoring group (who can be identified and contacted
through the Lakes and Streams Association in South Dakota).
Set up a classroom aquarium with organisms and water collected from a local lake.
Have students keep a journal on how the organisms were collected. Lead class
discussions on how each organism is dependent on other organisms. Have students
categorize the types of organisms collected and produced in your aquarium
environment. Upon completion of your aquarium habitat unit, return creatures to the lake
from which they came.
Create aluminum foil watersheds that include streams, lakes, and rivers. Sprinkle
pepper and drop some red, blue and green food coloring on different parts of the
watershed. Use a spray bottle to make it rain, and collect the runoff. What does it look
like? Where did the pollution come from? What can be done to clean it up? What could
have been done before it rained? How does this affect the turbidity of the lake in the
Algae: Aquatic plants (usually microscopic in size) that can grow as single cells or long
strands of cells
Eutrophication: The natural, physical, chemical, and biological changes that take place
as nutrients, organic matter, and sediment are added to a lake. When accelerated by
human-caused influences, this process is called cultural eutrophication.
Monitoring: To watch, observe and check especially for a special purpose
Nutrients: Something that nourishes or promotes growth and repairs the natural wastage
of organic life
Sediment: Materials or matter that settles to the bottom
Surface water: Water that is on top of the ground
Turbidity: The measure of water clarity or how much light can pass through water
Math, Social Studies, Science
SD Standards for 4th grade:
Deduction, Critical Thinking
Prior Preparation: Review the
"Watersheds: Where We Live" poster
included in the trunks. Discuss with the
class what watersheds are and how
lakes are a part of the "bigger picture".
Introduce water vocabulary from the
back of the poster and from this
algae, eutrophication, monitoring,
nutrients, sediment, surface water,