Green Lakes State Park

“Life is not measured by the number of breaths we take, but by the moments that take our breath away.” George Carlin

Deep, “Green,” And Meromictic: Glacial Jewels of Green Lakes State Park

Green Lake has 65 surface acres and is about 195 feet deep. Round Lake, a National Natural Landmark has 43 surface acres and is 170 feet deep. These pristine lakes, occupying glacially-carved basins, have many unique features, including unusual chemistry, shoreline reefs, and meromixis.

Green Lake – August 9, 2017

 

Green Lake – September 26, 2017

 

Round Lake – August 9, 2017

 

Round Lake – September 26, 2017

What is a Meromictic Lake?

Green and Round Lake are two of only a few lakes worldwide that do not experience “turnover,” or mixing of the upper and lower water masses. Several factors contribute to this complex and unusual condition known as meromixis. Differences in density and salinity between the upper and lower water masses; the lakes depths and surface areas; and their locations in deep basins with tree-rimmed shorelines that protect the water from strong winds are all conditions thought to help prevent turnover.

All the Colors of the Rainbow: Why the Lakes are Green

Green & Round Lakes – Often described as aquamarine or turquoise, their water is actually very clear. As you move along the lake trail, observe the water in different locations. You’ll enjoy all the color variations of blue and green.

As a light ray penetrates water, it separates into the spectrum of all colors of the rainbow. Each spectral color corresponds to a specific wavelength of light. The red wavelengths scatter little and are absorbed near the surface. The green and blue wavelengths pass through the clear water to a greater depth where they are reflected back to your eye.

Deadman’s Point: An Ancient But Living Reef

Although known as “Deadman’s Point”, this freshwater reef is both alive and growing! For thousands of years, microscopic organisms called cyanobacteria have lived in the reef’s surface, using sunlight and nutrients dissolved in the lake water to build the reefs. The nutrients are deposited on the reef, creating a type of limestone called marl that hardens to form the reef structure.

This unique and beautiful ecosystem is very fragile. Some organisms that live on the reef have existed on earth for millions of years. However, stepping on the reef can destroy them, and without these organisms the reef will no longer grow. Without the reef’s protective canopy, the plants and animals living underneath will also die.

The reefs along the shores of Green Lake provide homes for many organisms. The green and brown patches on reefs are microbial mats made by ancient organisms. Below the reefs, rare sponges and mosses grow from ledges and caves. The mosses provide hiding places and protection for fish and other animals.

Colorful and Busy Bacteria

Although bacteria are too tiny to be observed, here at Green Lakes the results of their activity may be seen and appreciated.

Approximately 55 to 75 feet below the lake surface is a three-foot thick layer of rosy-brown water created by the presence of photosynthetic purple and green sulfur bacteria.

At least three groups of bacteria that convert sunlight into food live in the lakes. At the surface, small cyanobacteria (cyano = blue) and diatoms (a type of algae) provide the main food source for zooplankton, which in turn provide food for other aquatic animals higher on the food chain.

Near the lakeshore, cyanobacteria combine with and precipitate calcium carbonate, forming interesting reefs around the lakeshore. The reefs provide a substrate for aquatic plants and shelter for fish.

Freshwater Reef – August 9, 2017

Freshwater Reef – September 26, 2017

 

Freshwater Reef – September 26, 2017

Round Lake: A National Natural Landmark

In 1973, Round Lake and 100 acres of the surrounding forest became our nation’s 182nd National Natural Landmark. This designation by the U.S. Department of the Interior is “reserved for resources that are sensitive and unique and which represent the natural heritage of our country.”

The lake which covers 34 acres and is 170 feet deep is of national ecological and geological significance due to its glacial origin, meromictic (non-mixing) character, and its adjacent old-growth forest. This forest, which has abundant bird life and some of the oldest trees in the country, may be seen southwest of the lake. Enjoy the spirit of this magnificent forest and lake setting as you explore this special environment.

Round Lake – August 9, 2017