Home » Our Work » Baykeeping » Nitrogen


Friends of Casco Bay has long been concerned about the impacts of excess nitrogen on the health of Casco Bay. Nitrogen is the necessary nutrient that promotes the growth of phytoplankton and seaweeds. An overdose of nitrogen in the ocean can trigger nuisance algal blooms that may reduce water clarity, prevent juvenile clams from settling, and suffocate animals in the mud. When these plants die, decomposing bacteria can deplete oxygen needed by marine life and create acidic conditions that make it harder for shellfish, such as clams, mussels, and oysters, to build and maintain their shells.

Over the years, we have seen intermittent scattered outbreaks of green slime, along streams outfalls and shorelines where we could trace over-applications of fertilizers up stream. In 2017, nuisance algal blooms around the Bay were larger and more numerous than in past years. In addition, we saw a dramatic increase in the occurrence of harmful algal blooms, including several species new to Casco Bay. These poisonous blooms may cause illness, memory loss, paralysis, and even death in marine life and humans. 

Why nitrogen is important

Nitrogen is essential for the growth of all living things. Nitrogen is one of the three most important “food groups” for plants. It is one of the primary components of fertilizer, along with phosphorus and potassium.

In the ocean, nitrogen is generally the critical element needed for plant growth. Algae, ranging in size from microscopic phytoplankton to sinuous seaweeds, form the base of the ocean food web. Excess nitrogen can stimulate algal growth beyond healthy amounts.

Why has nitrogen use gotten out of hand?

Photograph by Deb Dawson

Nearly 80 percent of the air we breathe is made up of nitrogen, but it is not in a form that land plants can use. For thousands of years, farmers relied on natural processes to convert nitrogen gas (N2) into a form that their crops could use. Farmers and gardeners compost crop and animal wastes to create natural fertilizer. They plant clover and other “nitrogen fixing” plants that extract nitrogen from the air naturally.

In 1909, a German chemist named Fritz Haber developed a process to synthesize ammonia (NH3) from the air, making it usable by plants. This form of nitrogen is highly volatile; nitrogen is a component of TNT and other high explosives.

During World War II, the U.S. government constructed ten new factories to produce ammonia for bombs. After the war, those factories produced ammonia for fertilizer—and fertilizer use exploded.*

This surplus of nitrogen coincided with the Green Revolution in farming, when scientists were working to develop new ways to feed burgeoning populations around the world. New varieties of high-yield plants were created, but they could not be sustained without fertilizers and irrigation. As the Green Revolution spread worldwide in the 1950s and 1960s, it significantly increased the amount of calories produced per acre of agriculture.♦

The availability and abundance of synthetic fertilizers led more farmers to concentrate on a few high-yield, high-cash crops, which required heavy fertilizer use. Many farmers abandoned the practice of crop rotation, which returned nitrogen to the soil naturally. The up side and the down side of the Green Revolution are that it has fed—and fueled—the world’s population explosion.

In recent times, we have seen an explosion in fertilizer used for ornamental purposes. Aggressive advertising promotes fertilizer use on residential properties. As a result, many home sites often feature huge swaths of fertilized lawns sloping to shorelines.

Where does excess nitrogen come from?

Nitrogen in the ocean can come from three main sources:

Runoff from farms, lawns, and city streets

Nonpoint sources of nitrogen in rainwater runoff and snowmelt can include soil erosion, pet wastes, and fertilizers. We are working to reduce excess nitrogen from several sources, working with individuals and communities to reduce or eliminate fertilizers for residential use. We are encouraging municipalities to pass ordinances to restrict the use of fertilizers on public lands and on private property.

Human sewage

Treated and untreated sewage and wastewater carry nitrogen, in the form of ammonium and nitrates, into our coastal waters. Large volumes of untreated sewage are diverted from the sewage transport system during heavy rain to prevent flooding the treatment facility. Untreated sewage may leak unintentionally (sometimes intentionally!) from broken pipes or undetected pipes.

Poorly-maintained septic systems and overboard discharge systems (OBDs) —antiquated household sewage treatment systems—can leak minimally treated wastewater into adjacent coves, resulting in the closure of coastal mudflats to shellfishing. While it is illegal to dump untreated waste into navigable US Waters, recreational boats can be a source of raw sewage if boat owners are not using special facilities or services to handle their waste. Since 1995, Friends of Casco Bay has operated a pumpout boat in order to reduce the likelihood of recreational sewage getting overboarded into the Bay.

With impetus from Friends of Casco Bay, several sewage treatment facilities are now working to reduce the amount of nitrogen released in their treated effluent water.

Air pollution from tailpipes and smokestacks

Nitrous oxide is released into the atmosphere by the incomplete combustion of fossil fuels. This noxious nitrogen gas can fall from the sky into the Bay.

How is excess nitrogen transported?

Rainwater and snowmelt drain water off roofs, parking lots, and city streets, flushing nitrogen into our waterways. Excess fertilizers from lawns, parks, playing fields, and farm land, can be picked and washed into streams and ultimately into the ocean. Soil erosion from development projects and bare spots on lawns also can transport nitrogen to the ocean.

Excess nitrogen flows through drains and ditches and down brooks, streams, and rivers to the sea. In addition, vast networks of pipes, some of which may be a century old, carry stormwater and wastewater into the Bay. Finding, tracking, repairing, replacing, and permitting discharges from pipes into our waterways are shared responsibilities of municipalities, the Maine Department of Environmental Protection (DEP), the US Environmental Protection Agency (EPA), the Clean Water Act, and watchdog groups such as Friends of Casco Bay.

Problems caused by excess nitrogen

Nuisance algal blooms

An algal bloom is a rapid increase in a population of algae. Algae are essential to a healthy ocean ecosystem, but too much of a good thing can become a bad thing. In 2017, we found “green slime” spreading across Back Cove in Portland, Mill Cove in South Portland, and Basin Cove in Harpswell. Thick mats of green algae coated mudflats, making life difficult for the marine life beneath. In places, algae prevented juvenile clams from settling and suffocated animals in the mud.

Harmful algal blooms that lead to shellfish closures

Excess nitrogen has been attributed to exacerbating harmful algal blooms (HABs). Casco Bay experienced a record number of shellfish closures in 2017, because of outbreaks of harmful algal blooms. We saw blooms of five different species of toxic algae in Casco Bay, some rarely if ever reported here before. These five species can cause illness, memory loss, paralysis, and even death in marine life and humans. In September, a toxic algal bloom in eastern Casco Bay killed nearly all the clams across 14 acres of mudflats.

Coastal acidification

The decomposition of dead algae adds carbon dioxide to our coastal waters. Acidifying seawater creates conditions that can further stress marine life.

Ocean scientists are finding that as seawater becomes more acidic, the shells of clams, corals, and tiny sea creatures at the base of the marine food web can become weakened and may actually dissolve. Acidic conditions can make it harder for Casco Bay’s clams, oysters, and mussels to build and maintain their shells.

Reduced water clarity

Eelgrass is often called the nursery of the sea because its roots and leaves shelter and feed so many of the ocean’s offspring, from eggs to juveniles and beyond. Eelgrass is a flowering plant rooted to the ocean floor, which thrives in clear, clean water. Large algal blooms can cloud the water, blocking the sunlight that eelgrass beds need to photosynthesize efficiently.

Degraded water quality

At several of our water quality sampling sites we have measured nitrogen at levels that exceed what the DEP considers healthy for marine life, especially eelgrass. When algal blooms die, bacteria decompose the dead plants, depleting oxygen that marine plants and animals need and releasing carbon dioxide into the water, increasing its acidity.

What is Friends of Casco Bay doing to limit nitrogen pollution?  


Working with partners to achieve reductions in nitrogen pollution  

Scott Firmin, Portland Water District’s Director of Wastewater Services, and Casco Baykeeper Ivy Frignoca

Friends of Casco Bay has been working with DEP, the EPA, and municipal governments to agree on meaningful nitrogen limits. In 2007, we helped persuade the Maine Legislature to pass a resolve that requires the DEP to draft a plan and timeline for developing nitrogen standards for Maine’s coastal waters.

We are now working with DEP, municipalities, and business, to set realistic levels for nitrogen in the discharge permits that the DEP and EPA issue to individual sewage treatment plants and industrial sites. The DEP reviews and renews these permits every five years, to regulate discharges from wastewater treatment facilities, stormwater pipes, and combined sewer overflows.

Working to eliminate Combined Sewer Overflows

Since 1993, Friends of Casco Bay has been prodding the City of Portland to fulfill a court-ordered agreement to fix its sewage and stormwater system overflow problem, and we applaud their progress. We serve on a stakeholder committee that oversees and comments on remediation plans.

Strengthening the MS4 permit

The Clean Water Act requires larger cities and towns to obtain a permit to develop stormwater management plans to reduce water pollution from storm drains, pipes, or ditches. Casco Baykeeper Ivy Frignoca is reviewing and commenting on drafts of the next MS4 permit that DEP will be issuing to municipalities. We want to ensure that the next five-year permit incorporates requirements aimed at eliminating illicit discharges, improving water quality in polluted streams, and reducing nitrogen pollution.

Reducing nitrogen in effluent waters

Sewage Treatment Plant courtesy of Portland Water District
Sewage Treatment Plant courtesy of Portland Water District

In 2017, Friends of Casco Bay forged an agreement with Portland Water District (PWD), which set a goal of reducing nitrogen in the effluent waters of PWD’s East End Wastewater Treatment Facility, estimated to be 2,437 pounds per day. It is expected that from May through at least October, nitrogen levels may be reduced by 20-40% from 2017 levels.

Adding Casco Bay streams to the impaired waters watch list

Periodically, we request that nitrogen-impaired parts of Casco Bay be added to the State’s Nonpoint Source Priority List, so those waters become eligible for funding to reduce pollution.

Addressing the impacts of climate change

Forging partnerships

We helped form the Maine Ocean and Coastal Acidification Partnership, which brings together fishermen, policy makers, advocates, and researchers to share data and identify steps we can take to mitigate and adapt to climate change.

Continuous monitoring

Continuous Monitoring Station

Our Continuous Monitoring Station gathers hourly data, 365 days a year, which will enable us to better assess how climate change may be affecting the chemistry of our coastal waters.

Supporting regional action to reduce carbon emissions

We support legislative bills and other efforts to keep Maine part of the Regional Greenhouse Gas Initiative (RGGI). RGGI is the first regional, cooperative, mandatory, market-based program in the United States to reduce greenhouse gas emissions by imposing a cap on carbon emissions from the power sector. Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New York, Rhode Island, and Vermont participate in RGGI. New Jersey and Virginia seek to join RGGI.

Maintaining a national presence

As a member of Waterkeeper Alliance, we join the chorus of member advocates calling for policies and actions at the national level to limit or mitigate the impacts of climate change.

Community Engagement

Working with communities to pass ordinances to limit lawn chemicals

By sharing our data on pesticides and nitrogen levels, educating city councilors about the risks of lawn chemicals, and serving on citizen task forces, we help municipalities work to adopt ordinances to limit lawn chemicals.

Two Casco Bay communities started developing their ordinances with the initial intent of limiting both pesticides and fertilizers. After finding that effort too ambitious, they opted for a step-by-step approach and worked first to ban synthetic pesticides. With our support, South Portland passed an ordinance in 2016 to restrict pesticide use. Executive Director Cathy Ramsdell served on the Portland Pesticide Task Force to help that city pass a similar ordinance in January 2018. 

Even though communities may start with restrictions on pesticide use, we reminded them that the most common all-purpose lawn additive is weed and feed, a product that contains several forms of pesticide and fertilizers. Now we are urging these communities to educate their municipal groundskeepers and residents on how and why to reduce the use of fertilizers and to implement ordinances limiting their use.

We continue to advise municipalities about the impact of lawn chemicals by providing scientific research that documents effects on humans, pets, and the ocean. We share considerations they may want to discuss as they craft their own ordinances, such as limiting use on public and/or private properties, phased-in or immediate implementation, defining and educating their target audiences, and deciding how to enforce or encourage compliance.


BayScaped Yard

Our BayScaping “neighborhood socials” engage and educate the community about nitrogen pollution. We teach residents how to grow green lawns that keep Casco Bay blue using ecological, chemical-free landscaping techniques.


Collecting data

Friends of Casco Bay has found high levels of nitrogen at most of the nearshore sites we tested and lower levels farther from shore. Water quality sampling has revealed that nitrogen pollution is more severe in areas that are closer to shore, near river mouths, at sewer outflow pipes, and other locations where stormwater runoff reaches the Bay. The further offshore we sampled, the better the water quality. This indicates that what we are doing on land is impacting the health of the Bay.

Besides making our own field observations of algal blooms, Friends of Casco Bay is collaborating with other researchers, government officials, and a network of volunteers to gather data to better understand these blooms.

Recruiting volunteers to collect data and share observations

We look to all Bay users to help us with our research.

Mac Richardson Nabbing Nitrogen Photo credit: Dave Dostie
Mac Richardson Nabbing Nitrogen
Photo credit: Dave Dostie

Nitrogen Nabbers: In 2016, nearly 100 volunteers lined the Fore River in Portland Harbor on July 10 at 10:10 a.m., to collect small vials of seawater. Our Nabbing Nitrogen “Flash Mob” collected valuable data on levels of nitrogen. Results revealed that areas where stormwater flows into Casco Bay had the highest levels of nitrogen. 

The event also showed us that there is a huge reservoir of goodwill at the ready, from people who want to help protect the health of the Bay and are willing to do that in short bursts of data collection efforts.

Water Reporters: We are beginning a new volunteer initiative to observe and share observations of algal blooms and slime-covered coves through our Water Reporter observing network for Casco Bay. Volunteer Water Reporters use a special smartphone app, or alternatively, a camera and a computer, to document, catalogue, organize, and share their observations of our changing Bay.  By reporting what they see, volunteers will be helping us investigate possible sources of nitrogen pollution and other problems.

How can you fight nitrogen pollution?

Personal lifestyle changes, as well as collective actions, can make a difference in our communities. Find out more actions you can take here

Collective action in your community

  • Lobby for and support a town ordinance to limit the use of water-soluble, synthetic fertilizers
  • Support (by funding) sewage treatment improvements
  • Support budgets and policies that protect science and acknowledge climate change.
  • Donate to support the work of Friends of Casco Bay to keep Casco Bay blue
  • Volunteer with Friends of Casco Bay

Around your home

  • Reduce or eliminate the use of fertilizers
  • Maintain your septic system
  • Burn less oil, wood, and coal to reduce pollution from smokestacks
  • Pick up pet waste and dispose of it properly

On the road

  • Reduce carbon emissions by driving less/sharing rides
  • Make your next vehicle one that gets better gas mileage
  • Keep your car tuned up to reduce pollution from tailpipes

On the Bay

Cover photo: Photograph by Deb Dawson

*“A Brief History of Our Deadly Addiction to Nitrogen Fertilizer,” Mother Jones, April 2013

https://www.motherjones.com/food/2013/04/history-nitrogen-fertilizer-ammonium-nitrate/ and

“Postwar Fertilizer Explodes,” Wessels Living History Farm, York, Nebraska


 ♦ Amanda Briney, “All You Wanted to Know About the Green Revolution: History and Overview,” Thought Company, May 17, 2017

More on Nitrogen and Casco Bay:  

Nab Data Suggest Land-Based Sources Contribute to Nitrogen Pollution

April 27, 2023

166 volunteers collected water samples from Portland Harbor to help measure and address nitrogen pollution. Here is what we found. It was a sweltering summer morning on August 7, 2022 when 166 volunteers descended on Portland Harbor to collect water samples for nitrogen analysis. After sending the 178 samples collected… Read more

Portland’s Landcare Ordinance Will Help the Bay

October 6, 2022

In great news for Casco Bay, the Portland City Council voted unanimously to limit the use of fertilizers in Maine’s largest city. On September 19, the council amended the city’s pesticide ordinance to become a landcare ordinance, which now includes policies that will: Prohibit the application of fertilizers within 75… 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 around the Harbor and collect simultaneous water samples. Read more

Maine’s Largest Wastewater Treatment Facility Keeps 1.5 Million Pounds of Nitrogen Out of the Bay

October 26, 2021

Following plant upgrades and improved techniques at Portland’s East End Wastewater Treatment Facility in 2017, struggling eelgrass beds near the facility’s discharge outfall have rebounded and we have observed a decline in nuisance algal blooms in lower Back Cove. Portland’s East End Wastewater Treatment Facility, the largest treatment plant in… Read more

Casco Bay is a No Discharge Area (NDA)

July 20, 2021

Casco Bay is a federally-designated No Discharge Area, which means it is illegal to release blackwater (raw or treated sewage) from any vessel into the Bay. All boats in Casco Bay must hold their blackwater until it can be removed at a pumpout facility. It is also illegal for any… Read more

Our top 10 moments of 2020

January 4, 2021

As this very odd year comes to a close, let’s celebrate the large and small ways our community helped us protect the health of Casco Bay in 2020. Here are our top ten for the year: 1.) On December 2, the Maine Climate Council released its four-year Climate Action Plan, “Maine Won’t Wait.” We… Read more