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Nuisance Algal Bloom Tracking

Nuisance and harmful algal blooms are an increasing concern in Casco Bay.

Friends of Casco Bay depends upon a network of more than 200 volunteer Water Reporters to  track the spread of the algae growth around the Bay. We use that information to alert the State, local municipalities, and others to changes in our coastal waters.

The map above shows the 100 most recent algal bloom reports around Casco Bay, as reported by Water Reporters.

Tracking large algal blooms can help Friends identify sources of excess nitrogen. An overdose of nitrogen can trigger excessive growth of nuisance algae, which smothers animals that live in mudflats, reduces water clarity, lowers oxygen levels, and causes acidic conditions that make it harder for clams and mussels to build and maintain their shells.

Casco Bay encompasses 200 square miles of water, has more than 578 miles of shoreland from Cape Elizabeth to Phippsburg, and includes hundreds of islands. We rely on our Water Reporters to know the details of what is happening around the Bay.  If you are interested in joining Water Reporter, you can learn more at cascobay.org/water-reporter or email volunteer [at] cascobay [dot] org.

Why is this happening?

All living things need nitrogen to grow, but too much nitrogen can turn Casco Bay from a healthy blue to a slimy green. An overdose of nitrogen can trigger the excessive growth of nuisance algae, reduce water clarity, and lower oxygen levels.

When the algae die, marine bacteria decompose the dead plants, depleting oxygen from the water and releasing carbon dioxide in the process. The resulting acidic conditions can make it harder for clams and mussels to build and maintain their shells.

Sources of excess nitrogen in coastal waters include fertilizers, sewage, pet wastes, decaying plants and animals, and emissions from tailpipes and smokestacks. Identifying the exact cause of green algae outbreaks is the challenge.

What is Friends of Casco Bay doing about green slime?

  • Friends of Casco Bay tests the waters throughout Casco Bay to document nitrogen levels.
  • Friends of Casco Bay is documenting the growth of algae patches around the Bay from week to week, and we solicit observations from others through Water Reporter.
  • We are using these reports to alert local and state officials and the news media to the extent of this issue.
  • Friends of Casco Bay is educating residents, municipalities, and lawn care providers on how to grow healthy lawns without applying nitrogen-laden fertilizers.
  • In 2007, Friends of Casco Bay helped persuade the Maine Legislature to pass a law requiring the Maine Department of Environmental Protection (DEP) to establish a limit on how much nitrogen may be discharged into coastal waters.  While this did not happen, we are working with the Department, municipalities, and businesses, to set realistic limits on nitrogen for discharge permits that the DEP and EPA issue to sewage treatment plants and industrial facilities.
  • The Portland Water District and Casco Baykeeper Ivy Frignoca negotiated an agreement aimed at reducing nitrogen pollution from sewage effluent. The collaboration helped the Maine Department of Environmental Protection develop a 139-page, five-year permit for the City of Portland’s East End Wastewater Treatment Facility, that better protects water quality. The $12 million upgrade to the plant’s aeration system may help reduce nitrogen in the plant’s effluent waters by 500 to 1,000 pounds each day! The aim is to reduce nitrogen loading in the discharges from the plant by 20-40% within five years. This is the first wastewater discharge permit in Maine to address nitrogen levels and is now a model for use in other communities.
  •  We are working with the City of Portland on its Combined Sewer Overflow Remediation Project that will reduce nitrogen-laden sewage overflows into the Bay.
  • Collaborate on revitalizing New Meadows Watershed Partnership in eastern Casco Bay to find an equitable, long-lasting solution to the poor water quality that causes massive algae blooms, low oxygen levels, and occasional fish kills in the upper New Meadows River
  • Our pumpout boat removes raw sewage from the holding tanks of recreational boats and transports for onshore disposal. For more information see our pumpout page.

What can you do about it?

History of our Algal Bloom Tracking 

Photograph by Instagram’s @mainedrone

On July 27th, 2016, we released a photo taken of Back Cove in Portland at our request by Maine Drone. It documented a disturbing development that our Executive Director Cathy Ramsdell first had noticed in early July: an expanse of green algae in the middle of Back Cove. As soon we posted this photo, people began reporting algae covered coves elsewhere. The image generated inquiries about Green Slime from print, radio, and TV reporters.

Abundant sunshine and high temperatures, along with ample amounts of nitrogen, created ideal conditions for thick mats of green algae to flourish, to the detriment of sea creatures underneath. Our own photos show that beneath the green algae, mud dwellers are struggling to survive in low oxygen and high acidity.

We thought the hot, dry summer of 2016 might have been an anomaly, creating ideal conditions for a green slime outbreak. But in 2017, Cathy again noticed green algae growth in Back Cove, even earlier in the summer. Starting on June 30, Friends of Casco Bay volunteer Deb Dawson of Deb Dawson Photography regularly took drone photos to provide visual evidence of green algae spreading throughout Back Cove. Deb continued to take photos tracking the change in growth that summer.

This photo of the algal bloom was taken on July, 17, 2017 by Deb of Deb Dawson Photography.
Back Cove August 2nd, 2017
Friends of Casco Bay volunteer Deb Dawson took this algal bloom photo over Portland’s Back Cove on Back Cove August 2nd, 2017 to document how much the green slime had spread. Photograph by Deb Dawson Photography.

Our Research Associate Mike Doan, Casco Baykeeper Ivy Frignoca, and our 2017 intern Emily Haggett confirmed sightings on some mudflats and shallow coves in Casco Bay. The areas with green algae blooms that summer were Mill Cove and Pleasantdale Cove in South Portland, Back Cove in Portland, and Basin cove in Harpswell. In 2017, we tracked algal growth at five sites.

In 2018, we expanded this effort and launched the use of Water Reporter. This created more effective and consistent reports, while created a low threshold way for more volunteers to take part in our work. Volunteers began signing up as Water Reporters in early August. More than 30 volunteers signed up around the Bay and many started sharing observations with us, including algal blooms.

In 2019, as the water warmed from spring through fall, volunteers in our Water Reporter observing network tracked algal blooms that appeared in 18 different locations around Casco Bay. The photos they took on their smartphones documented changes throughout the summer, as the algal blooms expanded to worrisome levels in many coves from Cape Elizabeth to Harpswell and West Bath.

Before 2020, we have not begun to see widespread nuisance algal blooms until late May or early June. On March 3, 2020, Casco Baykeeper Ivy Frignoca was shocked to see green algae growing at the base of the Spring Point seawall in South Portland. Soon after, our volunteer Water Reporters were posting images of green algal blooms in coves around the Bay. The spring and summer of 2020 were also an active year for algal blooms around the Bay, including a large bloom at Pleasantdale Cove in South Portland and  one in West Bath, among others.