A Healthy Hosmer?

As a skiing member of the Green Racing Project, one of my favorite summer work projects at Craftsbury is the weekly monitoring of water quality on Great Hosmer.  It is a great excuse to get out on the lake at least once during the week and enjoy the calm water, the sunshine and the loons. It also keeps me connected with my interests beyond biathlon; my favorite class in college was aquatic ecology. This summer I’ve been working with my GRP teammate Amy Glen to tackle this project. Every week, at least one of us goes out to collect the water data.


The “Milfoil Marauder.” COC’s trusty steed (well, most of the time) for invasive milfoil eradication efforts and for water sampling excursions.

Lakes age naturally through a process called eutrophication. As time passes, nutrient enrichment stimulates plant and algae growth in the water column. When this organic matter dies, it settles to the bottom of a lake along with suspended sediment, slowly filling it in. Vermont’s lakes represent a full range of natural eutrophic stages.

Illustrations from the Vermont Lay Monitoring Program Manual.

The youngest lake stage is oligotrophic- these lakes tend to be deeper, colder and less productive. Over thousands of years lakes naturally progress towards mesotrophic and eutrophic states. Eutrophic lakes tend to be shallower, warmer and highly productive. Normally we wouldn’t be able to see much change in our lifetime.  However, human activity can accelerate a lake’s aging process by introducing excess nutrients, particularly phosphorus, into the watershed. Upstream fertilizing, runoff, erosion and agricultural practices can all increase nutrient levels and consequently increase aquatic productivity. Higher plant growth and algae blooms can make the water slimy and murky, change the assemblage of fish and other aquatic organisms, and create undesirable conditions for swimming and boating. Cultural eutrophication (human caused) is the biggest threat to water quality in Vermont lakes.

The state of Vermont has been collecting water quality data from volunteer “lay monitors” on a number of lakes for over 30 years. Monitors measure 3 parameters of water quality: clarity, phosphorus and chlorophyll-a. This information provides base line data on lake water quality and documents changes over time. It is used by law makers and policy makers to help protect and preserve the lakes for our future enjoyment.

Water clarity is measured using a black and white Secchi disk. It is lowered into the water to the point when it can no longer be seen and that depth is recorded. Theoretically, higher amounts of algae in the water result in lower water clarity. Weather conditions can affect Secchi depth readings, so we try to sample on calm days whenever possible.


Former GRP member Chelsea Little takes an alumni secchi disk measurement.

Our collection equipment.

To measure the levels of phosphorus and chlorophyll-a, one must first do some sample collection. Water collection tools include a weighted hose tied to a rope, a bucket, and a couple of plastic bottles. The water samples we collect are analyzed by the state for phosphorus concentrations. Phosphorus is a limiting nutrient for plant and algae growth in most Vermont lakes; small increases in phosphorus often lead to large increases in lake productivity.


Processing water samples. I am on left and Chelsea is on right. Chelsea is an ecologist and former GRP racer who happened to be visiting on a sampling day and helped out.

Chlorophyll-a is a photosynthetic pigment found in all algae and green plants.  It can be used to quantify how much algae and plant growth there is in a lake. We use a simple filtration device to separate chlorophyll-a from a water sample. The paper filter is then collected by state scientists and analyzed.


Sometimes unexpected voyagers tag along in the boat.


Our rain gauge near the Touring Center. Rainstorms flush sediments and nutrients from upstream into the lake, so we note recent rainfall amounts in the sampling data.

So what have we learned in our measurements? Here is how Great Hosmer’s long term averages compare to other lakes in the state:

(Keep in mind Vermont has lakes naturally occurring in all different tropic states. This data is not a measurement of how “good” the lake is, but a measurement of what developmental state it is in.)

Great Hosmer has moderate to high water clarity…

… a high chlorophyll-a concentration…

… and a high phosphorus concentration.

Compared to other lakes it is eutrophic but has relatively clear water. In contrast, another local and familiar lake, Westmore’s Lake Willoughby, is oligiotrophic with lower productivity and very clear waters.

Here are Hosmer’s yearly averages from the past couple decades:
(TP stands for total phosphorous)

Great Hosmer’s water quality has remained relatively stable over this period, earning it a “good” on the Vermont’s Lake Score Card. It also earned a “good” in shoreline health, a “fair” in atmospheric pollution, and a “poor” in invasive species due to the presence of Eurasian Watermilfoil, a nuisance invasive plant. COC’s John Brodhead currently directs efforts to control Great Hosmer’s milfoil population through diving and pulling it up.

For more information on Vermont’s lake lay monitoring program and aquatic science, check out this website

May Great Hosmer stay beautiful for many more generations!

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3 Responses to A Healthy Hosmer?

  1. Mimi Grosser says:

    What about Little Hosmer? I’d really like to know where it stands on these measurements, even though we all know it’s eutrophic. Is it not being monitored? Those of us who live on its shore are always concerned about it.

    Very informative article. Thanks a lot!


    • sheldonm says:

      Mimi – Sorry for the delayed reply. At this point, the Center is only monitoring Big Hosmer Pond. My understanding is that VT Lay Monitoring Program will equip volunteers to do this sort of work. You can find more about that program here, and I’m sure the GRPers or John Brodhead would be able to answer questions as to how the process has worked for us.


  2. Pingback: Big Mama Earth Learning Academy » Local residents chronicle lake water quality

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