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Monitoring the Bay: Science that helps keep Casco Bay blue

We see water as fundamental habitat. Clean marine water makes the difference – for all species living in and on the Bay, including us! Improving water quality is the heart and focus of our work at Friends of Casco Bay. The water in the Bay is vulnerable to a wide and changing array of impacts – from pollutants entering the Bay to the effects of climate change.

It may be hard to believe today, but in the late 1980s, a report entitled “Troubled Waters” labeled Casco Bay as one of the most polluted estuaries in the nation. That report inspired a group of concerned citizens to form Friends of Casco Bay in 1989, to improve and protect the environmental health of Casco Bay.

Monitoring the water allows us to look at what lies beneath the beautiful views. We have been collecting data on the water quality of Casco Bay since 1992.  We have maintained and added to our data sets for over 25 years – one of the largest and most important long-term data sets on marine water quality in New England.

When we were founded, pollution was widespread, and the truth was that no one had a handle on the environmental health of the Bay.  So Casco Baykeeper Joe Payne launched our Water Quality Monitoring Program, enlisting and training staff and volunteer Citizen Scientists to “take the pulse” of Casco Bay, using proven scientific methods.

The reason we collect scientific data on the health of Casco Bay is to advocate for better protections and improvements in water quality. Our commitment to rigorously collected data is key to our credibility, as we advocate for policy and behavioral changes in our community. 

The Bay is changing, society is changing, and technology is changing. So we are asking new questions, shifting the ways we conduct our science and engage the public.

We are collecting data and observing changes to health of the Bay through the following projects:

Continuous Monitoring Stations

Photography by Kevin Morris

Our Continuous Monitoring Stations use the latest technology to collect data every hour, 24 hours a day, 365 days a year.* These stations are helping us understand the changing chemistry of our coastal waters and track trends over time.

Seasonal Sampling Across Casco Bay

Friends of Casco Bay Water Quality Sampling on the Baykeeper Boat.
Photography by Kevin Morris

Using our Baykeeper boat and truck, our staff scientists continue to add to our important long-term data set by collecting data at the surface and at profile sites at 22 locations every three weeks from May through October. Learn more about this seasonal sampling.

Nuisance Algal Bloom Tracking

Back Cove August 2nd, 2017
Photograph by Deb Dawson Photography.

Friends of Casco Bay is documenting the growth of algae patches around the Bay, and we solicit observations from others through Water Reporter, our observing network. Learn more about this algal bloom tracking.

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?”

Photograph by Kevin Morris • Aerial support provided by LightHawk

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.

Eposodic science efforts:

Microplastics Pilot Project

Photograph by Kevin Morris

We are looking at whether and what types of microplastics are in the Bay. Learn more about the impact of these tiny plastics.

Protecting Eelgrass Habitat

Restoring Nature’s Nurseries of the Sea

We are working with Maine Department of Environmental Protection, Casco Bay Estuary Partnership, and others to protect this important habitat.

You can help us tackle the biggest threats to the Bay!

Read more about our science work:

The State of the Bay: 50 years of the Clean Water Act and 30+ Years of Advocacy, A Casco Bay Matters Event

April 29, 2022

Please join us online on Wednesday, May 18, from noon to 1 p.m. for The State of the Bay: 50 years of the Clean Water… Read more

Join us for We Are Water

April 28, 2022

Join us on Wednesday, July 20, 5:30-8 p.m. for our We Are Water event where we will celebrate the 50th Anniversary of the Clean Water… Read more

Sign up for Nabbing Nitrogen, a Clean Water Act Day of Action!

April 27, 2022

Please join more than 100 other community members as we Nab Nitrogen in Portland Harbor on Sunday, August 7. That morning, volunteers will spread out… Read more

New data, NEW insight

April 14, 2022

Presenting data is like telling a story. When we look at a graph of our water quality data, it tells us a story about the… Read more

Bay temperatures rise as oxygen levels dip

January 18, 2022

Friends of Casco Bay has been collecting water quality data on the health of the Bay for 29 years. A recent analysis of our seasonal… Read more

Crabs, HABs, Sharks, and More… A Casco Bay Matters Event

January 10, 2022

Join us next Wednesday for an illuminating discussion with guest scientists who are doing cutting edge research in Casco Bay: Crabs, HABs, Sharks, and More… A Casco… Read more