Oscawana: A Dying Lake?

Part of the Young Naturalist Awards Curriculum Collection.

by Sarah, Grade 7, New York - 2003 YNA Winner
In the late 1960s, my great-grandparents visited a friend at his vacation house on Lake Oscawana in Putnam Valley, New York. At the time, this friend owned two adjacent properties, one of which was up for sale. He invited my great-grandparents up for a visit, hoping they would purchase the pristine property. While visiting, my great-grandparents fell in love with the lake and decided to buy the country house, picturing how much their son (my grandfather) and his children (my mom and siblings) would enjoy being there.

Back then, crystal-clear water from the lake supplied drinking water for the area. The lake provided its residents with many recreational uses, such as boating, fishing, and swimming. Today, however, Lake Oscawana is nothing like that. Its greenish, murky waters aren't as pleasurable to swim in, and slimy green algae can often be found floating in the water, interfering with the clarity of the lake. "Water clarity improved as Oscillatoria algae numbers decreased..." says limnologist George Knoecklein in his Lake Oscawana Monitoring Report 2000.

Lake Oscawana, a 386-acre lake, has the symptoms of a dying lake. By doing this project, I wanted to find out why and how Lake Oscawana has changed to become this way. Is there anything we can do to prevent this process or to help make the lake better? To investigate these questions, I journeyed to Lake Oscawana to try and find the answers.

Lake Oscawana
Lake Oscawana

It was a cold day in November when my dad and I set out in our two kayaks on Lake Oscawana. We decided to stay close to the shore since the water was shallower and clearer. It was easier to see fish and collect plant samples from the water. We explored three different sections of the lake: a cove, an area with many houses, and an area next to a forest. We had decided to start in the calm cove. I quickly realized that there was a lot of plant life in the water, more than I had seen in any other lake. This is a symptom of eutrophication, a process in which chemicals, such as phosphorous and nitrogen from fertilizers and road runoff, enter a lake and feed phytoplankton, one-celled algae, causing them to bloom and rapidly multiply. This abundance of phytoplankton gives the lake its murky green color.

Mussels filter out particles from the water.
Mussels filter out particles from the water.

In addition to this, the phytoplankton block sunlight from getting to the plants that live on the bottom of the lake. Eventually, some of these submerged plants die, reducing the habitats for fish and other aquatic animals. When these plants die, bacteria break them down. During decomposition, these bacteria consume large amounts of oxygen, which is removed from the water. This process is called deoxygenation. As a result, aquatic animals struggle even more to survive. It is important to preserve the fish in lakes. The fish in freshwater have a very high diversity. Although freshwater makes up less than 5 percent of the water on our earth, roughly 40 percent of all fish species inhabit freshwater.

Another quality most eutrophic lakes share is a high surface-to-volume ratio. This means that the surface area of the lake is large compared to its depth. Although very deep lakes have this quality, eutrophic lakes usually have higher ratios than the average healthy lake.

As we moved on, we collected samples of a few different kinds of plants that were floating in the water. They all had different-shaped leaves, and most of them had algae attached to them. I also found an empty freshwater mussel shell. It was open, but the two halves were still attached. The shell itself was black, but the inside was white with a pinkish tint. Mussels are good for the lake because they filter out algae and particles from the water.

On one certain section along the shore I noticed that there were many lily pads in big groups. I had seen them before, floating in large numbers on the surface of the water, especially in the summer. As far as I have seen, they only grow in certain shallow parts of the lake, such as the cove we were in.

The Eutrophication Process
The Eutrophication Process

As we traveled along the developed shoreline, the waters were too deep to look for plant life. However, I remembered from swimming in this area of the lake last summer that many plants tickled my legs. I also discovered a pipe leading up to a road. I noted this because it probably carried harmful runoff containing oil, gasoline, and wiper fluid from the road. I think the contents spewing from this pipe are likely to have adverse effects on the lake and could be contributing to pollution.

Another way that humans can accelerate the death of a lake is by developing areas along the shore. When the shore is a lawn, fertilizer and chemicals can flow into the lake at a quicker rate than if they had to flow around trees, shrubs, and rocks. Also, when the runoff meets obstacles, such as tree roots and layers of leaves or sand, impurities are filtered out, resulting in less phosphorous (P) and nitrogen (N) getting into the lake.

The rest of our exploration of the developed side was uneventful. There were hardly any plants to observe. We decided to head over to the forest side. On that side, the water was shallower, so it was easy to observe what was in the water. We added a few more plants to our collection, including one with wide, pointed leaves and a thin stem. I also found a stick covered in algae. It was slimy and gross, but I decided to keep it anyway. Another interesting thing I found was lily pads. These, however, were completely different from the other ones. First of all, these were brown. They had thicker stems and thinner leaves that came to a point. I had never seen this kind before. I discovered later that they are pickerelweeds.

Comparing the Depths of Lakes
Comparing the Depths of Lakes
Distribution of Fish Species
Distribution of Fish Species

After a few hours of exploring, we decided to leave. We had a large collection that I could study later. It was also getting very cold. It took us a while to pack up our stuff. We had to move the items we had collected into a bucket, which we filled with lake water. Once my dad had gotten the kayaks out of the water, we took a few trips to load everything into the car. Not long after, we were on the long drive home.

Afterward, I did research on the plants I had found and on the history of the lake. I found out many interesting facts about the plants I had collected.

Although I was not able to specifically identify each plant as I had planned, I categorized them. There are four different categories into which aquatic plants are sorted: algae, submerged plants, floating leaf plants, and emergent plants. They all live in the littoral zone, or the area near the shore of the lake where it is shallow. Algae plants have no roots, float in water, and range from having one cell, like phytoplankton, to many cells, such as chara. I found a lot of algae on my trip. I found one floating around by itself, and many others attached to sticks and other plants. 

Runoff from the road and fertilizer runoff from lawns further pollute Lake Oscawana.

Submerged plants are usually rooted to the bottom. Their leaves and stems grow entirely underwater. I found that there were a lot of these plants in the lake, but only a few species. This is true for many eutrophic lakes. The number of plants is high, but the diversity is low.Floating leaf plants are rooted to the bottom but have leaves that float on the top. Lily pads and pickerelweeds are the only examples of plants I found in this category. Lily pads only grow in areas where there is little wave action. The shallow cove is protected from the wind and there is less boat activity in there. This may be the reason I found more lily pads growing there.

The last category is emergent plants. They are rooted to the bottom, but their leaves and stems extend out of the water. They grow along the shore where the water is shallow. The only emergent plant I saw was a dry, brown plant that grew in the cove. It looked dead because of its tan color, but will come "alive" in the spring.

I also wanted to find out if the local residents were doing anything to help the lake. I discovered a local newsletter, the L.O.C.A. (Lake Oscawana Civic Association) News. I read many articles of interest showing the steps that are being taken by L.O.C.A. to help save the lake. Even though L.O.C.A took action to improve the lake nearly 30 years ago, Lake Oscawana is nowhere near being fully healthy.

Types of Plants in the Littoral Zone
Types of Plants in the Littoral Zone

L.O.C.A. is still taking steps to further help the lake. Their major concern is milfoil, a plant that can easily dominate the entire lake. For example, they warn boaters to avoid very shallow areas of the lake with a lot of plants. A motorboat's propeller cuts up milfoil, sending fragments floating to the top. When a piece of milfoil is floating on the surface, it drops seedlings that root into the bottom and grow into a multitude of milfoil. They even warn other boats such as canoes and kayaks to avoid those areas, because paddles can also uproot milfoil. They also request that if you see milfoil floating in your swimming area, you remove it from the water.Another concern is the alewife. The alewife is a fish that was introduced to the lake by fishers who used them as bait. The alewife's presence is a negative factor in the health of the lake. Their main food source consists of zooplankton. Zooplankton are helpful to an eutrophic lake because they eat algae. To control this problem, walleyes were introduced into the lake. They feed on other fish, primarily the alewife. Walleyes are also commonly known as pike, pickerel, and jackfish. Fishers are warned to release any walleyes they catch so that they can continue eating alewife and help the lake.

All of these actions are helping the lake. I hope that the lake will improve so that my children and grandchildren can enjoy its beauty and recreational uses, as my great-grandfather envisioned. By doing this project, I have discovered more about the lake I have known and enjoyed my entire life.

Sarah found many different plants, including lily pads and pickerelweeds.
Sarah found many different plants, including lily pads and pickerelweeds.

I have concluded that Lake Oscawana is being affected by eutrophication. However, my original question still remains: is Lake Oscawana a dying lake? This project has taught me that dying is a natural process that many lakes go through. However, in some it happens faster. My real question should be: how fast is Lake Oscawana dying? Although I can't really answer that question, I can say that Lake Oscawana appears to be further along in the process.

I know what I can do to slow down the process. I can remove milfoil from the lake and avoid boating in shallow waters where my paddle stirs up the bottom. I can also release any walleyes I catch so that they can continue eating alewife. More importantly, I can educate lake residents about how they can also help the lake. Although each action may not be a lot by itself, put together, who knows what it could add up to. As George Knoecklein (a limnologist) said in an e-mail response, "Everything they do affects the lake in some way, maybe small, but it still has an effect."



Web Sites

"Eutrophication." November 7, 2002. University of Manitoba. Retrieved from the World Wide Web on November 25, 2002: http://www.umanitoba.ca/institutes/fisheries/eutro.html."

The Impact of Phosphorous on Aquatic Life: Eutrophication." 2001. SciLinks. Retrieved from the World Wide Web on November 19, 2002: http://www.agnr.umd.edu/users/agron/nutrient/Factshee/Phosphorus/Eutrop.html.

Koller, David. "Eutrophication." July 7, 1993. Wetlands Education System. Retrieved from the World Wide Web on November 19, 2002: http://agen521.www.ecn.purdue.edu/AGEN521/epadir/wetlands/eutrophication.html.

Mandaville, S.M. "Soil & Water Conservation Society of Metro Halifax." February 4, 2000. Retrieved from the World Wide Web on November 19, 2002: http://lakes.chebucto.org/eutro.html#Introduction.

"Walleye." February 9, 2002. Creative Publishing International. Retrieved from the World Wide Web on December 4, 2002: http://www.pvisuals.com/fishing/species/walleye.html.

"Where Aquatic Plants Grow." 2002. Minnesota Department of Natural Resources. Retrieved from the World Wide Web on December 1, 2002: http://www.dnr.state.mn.us/shorelandmgmt/apg/wheregrow.html.



Abramovitz, Janet N. Imperiled Waters, Impoverished Future: The Decline of Freshwater Ecosystems. Washington D.C.: Worldwatch Paper, 1996.

Agsteribbe, Marcel, William A. Andrews, Daniel G. Stoker, and Nancy R. Windsor. A Guide to the Study of Freshwater Ecology. Engle Wood Hills, New Jersey: Prentice-Hall, Inc., 1972.

Brnmark, Christer and Lars-Anders Hanson. The Biology of Lakes and Ponds. New York: Oxford University Press, 1998.Cresser, Malcolm and Anthony Edwards. Acidification of Freshwaters. New York: Cambridge University Press, 1987.

Duffey, Eric. Conservation of Nature. New York: Collins Publishers and McGraw-Hill Book Company, 1970.

Engstrom, Paul H., Steve J. Gadler, and Claire Jones. Pollution: The Waters of the Earth. Minneapolis: Lerner Publications Company, 1971.

Jeffries, Michael and Derek Mills. Freshwater Ecology: Principles and Applications. New York: John Wiley & Sons, 1990.

The Oxford Dictionary of Quotations: Third Edition. New York: Oxford University Press, 1979.

Smith, Robert Leo. The Ecology of Man: An Ecosystem Approach: Second Edition. New York: Harper & Row Publishers, 1972.

Tesar, Jenny. Endangered Habitats. New York: Facts on File, Inc. and Blackbirch Graphics, Inc., 1992.


Newsletters and Reports

Green, Arlene. L.O.C.A. News (Spring 1990): 2.

Green, Arlene. L.O.C.A. News (Summer 1990): 1-2.

Green, Arlene. L.O.C.A. News (Summer 1991): 1, 3-4.

Knoecklein, George W. Lake Oscawana Annual Monitoring Report 2000 (December 8, 2000): 4.McLaughlin, Kathleen. L.O.C.A. News (Fall 1991): 3.