Following on the heels of last week’s column about water quality in Casco Bay and the efforts that are being made both to measure it and to reduce the impacts of what we do on land upon the health of what is in the water, I wanted to follow up this week to give a little background on what is being done locally to assess water quality and why it is so important to what lives under that water.

First, measuring water quality is not simple. It involves multiple components and some sophisticated equipment. Together, an array of measurements helps scientists and managers to understand what is happening in the water and what might be causing changes that are observed. There are some simple components of these measurements like temperature, but even this can be complicated as it depends where in the water column you take the temperature of the water. At this Monday’s presentation at the Town Council meeting (recording available on local cable), Friends of Casco Bay’s Science and Advocacy Associate Heather Kenyon pointed out that there was a significant difference between surface water and water closer to the seafloor in Maquoit Bay last summer. This differentiation between layers of water, called a thermocline, can prevent water from mixing, which is an important way that oxygen gets circulated throughout the water column. This is likely one of the factors that contributed to the algal bloom in the bay.

An algal bloom in Maquoit Bay discolored the ocean water and shoreline in the summer of 2022. The lack of mixing between water layers is one factor that prevents oxygen circulation, which can cause algal blooms. Courtesy of Glenn Michaels

In addition to temperature, dissolved oxygen, as mentioned above, is another critical measure of water quality, as it is essential to the life that the water supports. PH is another component that assesses the acidity of the water — something of concern as oceans become more acidic, which impacts things like the ability of shelled organisms to adequately maintain and grow their shells. Nitrogen is yet another important measure. While having plenty of nutrients might seem like a good thing, a good point that FOCB’s baykeeper, Ivy Frignoca, made is that having too many nutrients in the water can result in algal blooms. This can often be the result of input from the shore in the form of sewage outflow or runoff of land-based fertilizers. There are many more measurements in addition to these, but that is a rundown of some of the major components.

Given that these measurements can be quite locally specific, it takes a lot of effort to adequately cover the waters of Casco Bay. To that end, multiple groups work together to collect this data. At the state level, the Maine Department of Marine Resources’ Public Health Division is responsible for measuring water-quality components that specifically impact the health of the shellfish resource in order to open and close harvesting areas when the conditions might make the shellfish unsafe for human consumption as part of the National Shellfish Sanitation Plan.

Among the many direct impacts that water quality has on marine life, that to the shellfish resource is perhaps the most direct and obvious. Following a significant rainfall, you can go to the DMR’s map at to see the harvesting closures that result from land-based inputs.

In addition to the DMR, Brunswick’s town staff take water quality samples throughout the year at specific locations. They will be out this spring collecting data off Brunswick’s coast at a number of sites. And Friends of Casco Bay’s scientists have multiple sampling sites, including those where they have consistent monitoring throughout the year thanks to their Continuous Monitoring Stations that are equipped with sophisticated data-collection devices in three locations throughout the bay.

As we get deeper into the spring and activity near and on the water increases, this is a good time to be aware of the connection between land and sea and all of the efforts being made to better understand how we can ensure the health of our coastal waters.

Susan Olcott is the director of operations at Maine Coast Fishermen’s Association.

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