Data collected through these efforts (varies depending on project) include:

• Direct measurements: temperature, salinity, dissolved oxygen, pH, chlorophyll, depth, partial pressure of carbon dioxide, color
• Derived calculations: alkalinity, dissolved inorganic carbon, calcium carbonate saturation state
• Analyses of water samples: total nitrogen, dissolved inorganic nitrogen (nitrate and nitrite, ammonium, silicate, phosphate)

From “How healthy is the Bay” to “How is the Bay changing?”

Our Citizen Stewards Water Quality Monitoring Program was a signature effort of our work for more than 25 years.  The program was designed to help address the questions “How healthy is Casco Bay?” and “What areas of the Bay are challenged in terms of water quality?” The data collected, along with data collected by staff, provided snapshots of conditions around the Bay. The data were fundamental and foundational, helping us to address those questions, leading to both the design of the Casco Bay Health Index and the release, in 2015, of the report “A Changing Casco Bay”.

The processes of analyzing our data led us to the realization that the question we now want and need to be asking is fundamentally different: “How is the Bay changing?”

In order to address that question with statistical integrity, we need higher frequency data than these “data snapshots” provide. Technology, in the form of data sondes with various, carefully calibrated probes and sensors, makes it possible to collect much more frequent and more detailed data that can allow us to look for trends in the health of the Bay.

You can learn more about our science efforts by going to our Continuous Monitoring Station page, our Seasonal Sampling Across Casco Bay page, and the page for Water Reporter. 

What the science has been telling us

• Casco Bay is generally healthy – compared to other estuaries.
• The most environmentally challenged areas in Casco Bay are Portland Harbor, the New Meadows embayment, and the mouth of the Harraseeket River.
• The healthiest regions of the Bay are Broad Sound, Maquoit Bay, Middle Bay, and the offshore waters near Halfway Rock.
• Land-based origins contribute significant sources of excess nitrogen.
• Bottom water in the Bay is becoming more acidic, a worrying trend that mirrors what is happening worldwide .
• The warmest time of year is getting warmer; summer is lasting longer in Casco Bay, with temperatures rising and staying warmer longer into the fall.
• In order to better understand how the Bay is changing, we needed to increase the frequency of data collection—so we launched our Continuous Monitoring Station.

You can learn more about the health of specific areas of Casco Bay by using our Interactive Casco Bay Health Index . This is an easy to interpret, visual guide to the health of the Bay, based on a subset of the historical data collected through our Citizen Stewards Water Quality Monitoring Program (1994 – 2017). You can compare 37 sampling sites around the Bay and learn about what affects water quality at each site.

Nitrogen levels are high close to shore, likely due to an excess of this nutrient flowing from lawns, fields, sewage systems, and stormwater runoff.  Air deposition of nitrogen and offshore sources contribute, as well. Too much nitrogen in the marine system turns it into a pollutant, which can trigger nuisance algal blooms which can smother shorelines with mats of bright green algae, choking out life beneath it. Some harmful algal blooms can be triggered by too much nitrogen,  threatening human and marine health, resulting in closures of shellfish harvesting.

Our data are telling us that the chemistry of Casco Bay is changing.  Our waters are becoming less alkaline and more acidic. This is bad news for clams, mussels and oysters – and for those who make their livelihoods from growing and harvesting these resources.

How our data have been used

Our data and observations have been used for many purposes, by our staff and other researchers, agencies, organizations, and individuals. Our data are used to:

• Upgrade water quality classifications in sections of the Bay
• Identify challenged areas of the Bay
• Identify pollutants entering the Bay [for example, excess nitrogen and pesticides]
• Regulate and reduce pollution through state-issued discharge permits
• Influence legislation and local ordinances
• Enable state government to document the health of Maine’s coastal waters
• Inform our community engagement, from educating folks about the Bay to recruiting volunteers who want to “get their hands wet”
• Ensure better long-term protections for the Bay
• Assist in the education of future oceanographers, marine science and marine policy makers
• Advance science in Maine
• Assist others in their scientific investigations and in other innovative ways

Learn more about our data and how it is used by clicking here.

As the threats to our coastal waters continue to change, we will continue to keep an eye on the health of the Bay.