When the Lake Association was founded in the 1980s, invasive fanwort — Cabomba caroliniana — had taken over large areas of Chebacco Lake’s shallow-water zone.

Swimmers complained of getting caught in the weeds, while fishermen regularly found their hooks tangled in dense vegetation.

Public funding was secured relatively quickly, leading to the first diagnostic study of Chebacco Lake. The “Lycott Study,” released in 1985, created what is now an invaluable baseline for understanding changes in lake health over the past four decades.

The source establishes the 1985 Lycott work as the baseline for the lake's modern scientific history.

Lycott initially recommended hydro-raking Cabomba from recreational and residential areas. In practice, the approach proved to have little effect even in the short term.

More importantly, the study concluded that Cabomba was a symptom of a much larger problem: eutrophication.

Eutrophication occurs when excessive nutrients enter a water body and encourage excessive plant and algae growth.

The consultants warned that the natural progression from lake to swamp might ordinarily take hundreds or even thousands of years. For Chebacco Lake, however, they feared that nutrient overloading could accelerate that process dramatically.

Phosphorus was identified as the primary concern, particularly phosphorus entering the watershed through human waste, lawn fertilizer, and household detergents.

Outflow from septic systems was Lycott’s greatest concern.

The PDF specifically identifies phosphorus and septic-system outflow as central concerns from the 1985 study.

In 1998, two biology professors from Salem State College conducted a follow-up study.

They repeated sediment-core sampling performed during the Lycott study and found encouraging news: sediment thickness at the bottom of Chebacco Lake had not materially increased during the 13 years between the two studies.

But the broader conclusion remained the same.

Nutrient overloading was still at the heart of the lake’s problems.

The Salem State study emphasized that there is no single solution to lake vegetation problems.

Both short-term and long-term management require a multi-faceted approach that considers the lake’s geology and biology as well as land use and development throughout the watershed.

The researchers also called for renewed public education and watershed management focused on reducing nutrient loading.

Their message was clear: without addressing the underlying movement of nutrients into the lake, treatment of the symptoms alone would be short-sighted and waste resources.

That final point continues onto page 3 of the source.

Much like the human body, a lake has measurable vital signs that help us understand its overall health.

For Chebacco Lake, four important indicators are:

• Water clarity
• Dissolved oxygen
• Nutrient levels
• Phytoplankton, the microscopic plants living in the water

To measure these vital signs, CLWA began working with limnologist Hillary Kenyon Garovoy of Applied Watershed Sciences.

A reliable diagnosis requires multiple years of sampling and analysis. The 2023 results therefore provide important insights and warning signs, but they should not yet be treated as a final diagnosis of the lake’s long-term condition.

The source identifies these four indicators and explicitly cautions that multiple years of sampling are needed.

Aquatic plants depend on sunlight in much the same way that plants on land do.

The amount of sunlight reaching underwater plants depends heavily on how clear the water is.

When water clarity declines, less light reaches aquatic vegetation. This can mean fewer plants, less food for animals, and less oxygen being produced within the lake.

Cloudy water may result from suspended sediment, algae, and other materials in the water.

This explanation comes directly from the water-clarity discussion. Know Your Watershed II - How He…

The dissolved oxygen results are particularly concerning because shallow lakes like Chebacco are vulnerable to oxygen-depleted areas near the lake bottom.

These “dead zones” can reduce usable fish habitat and create conditions favorable to algae blooms.

They can also trigger another serious problem: internal phosphorus loading.

When oxygen disappears near the lake bottom, phosphorus that had been bound in sediments can be released back into the water.

That means some of the nutrient problem may come not only from phosphorus entering the lake from the watershed, but also from phosphorus already stored within the lake itself.

The PDF introduces the term “internal phosphorus loading” specifically in this section.

Both phosphorus and nitrogen were measured at extremely high levels during the 2023 sampling.

At this stage, there is not enough long-term data to determine exactly how surface-water nutrient concentrations have changed over time.

However, the dramatic increase in phosphorus and nitrogen measured near the bottom at the sampling sites may indicate that internal phosphorus loading is occurring.

Phytoplankton are microscopic plants that form an important part of the lake ecosystem.

The 2023 analysis indicated that high water temperatures combined with high nutrient levels can give cyanobacteria a competitive advantage over other, more benign phytoplankton groups.

Some cyanobacteria can produce harmful algae blooms.

Fortunately, cyanobacteria were not dominant at the time of the 2023 sampling despite the very high nutrient concentrations.

The findings do not indicate that a harmful bloom is currently occurring, but they reinforce the importance of continued monitoring.

The initial 2023 findings helped guide continued monitoring in 2024.

At this stage, the evidence points to a lake vulnerable to another harmful algae bloom similar to the bloom that closed Chebacco Lake for 19 days in 2020.

Reducing the nutrient imbalance should also reduce that risk.

But restoration and preservation decisions require more data and analysis before major investments are made.

The source connects nutrient imbalance with the risk of another bloom, while still emphasizing the need for additional science. Know Your Watershed II - How He…

The answer is mixed.

There are several encouraging signs.

Chebacco Lake has not experienced a harmful algae bloom since 2020.

E. coli counts, which help indicate whether the lake is safe for recreational contact, have consistently remained very low.

Petroleum residue has not been detected in lake-sediment sampling.

The 2024 alewife run counted 36,685 fish, the third-highest count recorded in more than a decade.

Save Chebacco has also led an extensive campaign to forestall development at 133 Essex Street.

These are all identified as positive indicators in the article. Know Your Watershed II - How He…

That is the challenge before us.

Chebacco Lake still provides extraordinary recreational, ecological, and community value, but the scientific evidence shows that protecting it requires continued monitoring, better understanding of nutrient movement, and action throughout the watershed.

Our goal is not simply to respond when a problem becomes visible.

It is to preserve a healthy lake and watershed for generations to come.

The source ends the main article with preservation for future generations as its call to action.