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Water Clarity/ Secchi

Since 2008, GCWIN has managed lake clarity monitoring in Grand Lake and Shadow Mountain Reservoir.  Currently, 7 sites are monitored every week from ice-off to ice-on.  The information gathered is used by the Grand Lake Adaptive Management Committee to evaluate how operations of the Colorado-Big Thompson Project can be adapted to improve Grand Lake clarity.


This symbol indicates the site locations for all 7 water clarity measurements

An underwater camera is used at these sites

Chlorophyll A and phytoplankton samples collected at these sites

What is this data, and what does it mean?


Water clarity is a measure of how deeply visible light penetrates through water. It is directly related to the total suspended solids (TSS) is a body of water; clear waters will have less TSS, while turbid waters will have more. This is important because it determines how much sunlight is able to reach submerged aquatic vegetation, producing oxygen that helps create a viable habitat for other aquatic life, which has implications on the health of the aquatic ecosystem as a whole.

Water clarity can vary depending on wind patterns, storms, and even changes in sunlight, and some bodies of water are naturally turbid. However, human activity can also have a large impact on clarity. Waters that receive an excess of nutrients from fertilizer runoff or sediment deposits from construction can experience an increase in turbidity. Because of the importance of water clarity on the health of the ecosystem and its susceptibility to frequent change, it is vital that we monitor it as a measurement of the water quality of Grand Lake and Shadow Mountain Reservoir.


Chlorophyll is vital for plants to photosynthesize, and chlorophyll a is the main type found in green plants and algae. Measuring this compound can help us determine how much algae is growing in a body of water. While algae is a natural occurrence in freshwaters, too much of it can cause problems for the ecosystem, as well as aesthetic problems impacting recreation.

Increased algae growth is caused by an increase in nutrients that can come from fertilizers, septic systems, and/or sewage treatment plants. The excess algae causes a decrease in dissolved oxygen, which has a detrimental effect on the wildlife inside the waterbody. 


Phytoplankton are free-floating, microscopic algae that are capable of photosynthesis, making them an important food source for other organisms, such as small fish. They are uniquely adapted to their environment: nutrients, habitat, specific depth, and chemical condition. Studying their relative diversity and taxonomic richness helps us understand the biological condition of these two waterbodies.

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