Home » dissolved oxygen

Tag: dissolved oxygen

Action alert: Casco Bay & Presumpscot River need your voice!

Photo provided by Michael Shaughnessy, Friends of the Presumpscot River.

The Presumpscot River and Casco Bay need your voice!

2022 marks the 50th Anniversary of the Clean Water Act. We can think of no better way to celebrate than to see the lower Presumpscot — the biggest tributary to Casco Bay — upgraded to a Class B water.

Please help us make this happen by letting a key committee of the Maine Legislature know that you support an amendment to: “LD 1964 An Act To Update Certain Water Quality Standards and To Reclassify Certain Waters of the State.”

Under the Clean Water Act, bodies of water are classified as Class AA, A, B, or C based on their health. Class AA and A waters are the healthiest and receive the highest protections while Class C waters allow for some modification to natural conditions caused by human activity. Upgrading a body of water’s classification matters because it strengthens the legal protections it receives.

As written, LD 1964 lacks language to upgrade the lower Presumpscot River, from Saccarappa Falls in Westbrook to head of tide between Portland and Falmouth, from Class C to Class B. We are working to fix this.

Thirty years ago, the lower Presumpscot was called the “dirtiest little section of river”¹ in Maine. Back then, it could not even meet the Class C water quality standard. Today, the Presumpscot is the jewel of downtown Westbrook. The river supports ever increasing numbers of fish and wildlife. In recent years, local residents have even spotted sturgeon jumping from its waters — a sure sign of a healthy river as sturgeon are highly sensitive to pollution. People, too, are once again using the river for swimming and other forms of recreation.

On top of all of these improvements, Friends of Casco Bay and others have reviewed water quality data from the lower Presumpscot River and concluded that it meets the Class B standard. We want to lock in these improvements in water quality and make sure there is no back-sliding to Class C. The Clean Water Act forbids degrading water quality, and aspires to continually restore and upgrade waters to higher classes.

The Maine Legislature’s Environment and Natural Resources Committee will hold a hearing on LD 1964 on February 28 at 9 a.m.

Casco Bay needs you to submit written testimony in support of an amendment to the bill that will upgrade the lower Presumpscot to Class B.

It is important that the Committee hear from you. Use the toolkit below to submit your testimony.

Thank you for using your voice to help protect the health of Casco Bay,

Ivy Frignoca
Casco Baykeeper
Friends of Casco Bay

¹ Robert M. Sanford and William S. Plumley, River Voices (North Country Press, 2020), p. 239.

Testimony Toolkit to support and amend LD 1964

Below are suggested talking points you might want to include in your testimony. Legislators appreciate hearing your personal story, including what the Presumpscot River and Casco Bay mean to you.

Suggested testimony (feel free to put in your own words):

Dear Senator Stacy Brenner, Representative Ralph Tucker and Distinguished Members of the Environment and Natural Resources Committee,

I am writing to ask that the Environment and Natural Resources Committee vote that LD 1964: An Act To Update Certain Water Quality Standards and To Reclassify Certain Waters of the State, ought to pass with an amendment to upgrade the lower Presumpscot River, from  Saccarappa Falls to Head of Tide, to Class B status because:

  • The Clean Water Act aspires to restore water quality and urges us to set the highest attainable water quality classifications for all bodies of water. These expectations should now receive particular emphasis as 2022 is the 50th anniversary of the Clean Water Act. 
  • The lower Presumpscot River was once known as the “dirtiest little section of river in the state.” Industrial pollution contributed high loads of toxins and caused dissolved oxygen levels to plummet. Dams degraged river habitat, including blocking fish passage. This all began to change when local residents and Friends of the Presumpscot River took it upon themselves to shine the spotlight on the importance of clean water. Stronger permit requirements for the S.D. Warren paper mill, water quality upgrades for upriver sections of the Presumpscot, dam removal, and fish passages have helped the river achieve a dramatic recovery. Today, the river lies at the heart of downtown Westbrook, and supports flourishing neighborhoods and recreation in nature reserves. Anadromous fish have returned to run up the Presumpscot and local residents have witnessed sturgeon jumping from its waters. 
  • In the summer of 2021, the Maine Department of Environmental Protection (DEP) collected data from the lower Presumpscot. Those data show that the lower Presumpscot maintained dissolved oxygen saturation well above 75%, a benchmark that demonstrates the river meets Class B standards


[Your name]

How to submit your testimony:

The Maine Legislature’s Testimony Submission and Sign-up page can be confusing to navigate. Please follow the instructions below to submit your testimony.

  • Go to https://www.mainelegislature.org/testimony/ 
  • First select “public hearing” as the type of hearing. 
  • Then select “Environment and Natural Resources Committee” and identify the specific date and time when the bill hearing is scheduled (LD 1964 will be heard on February 28 at 9 a.m). 
  • You will then have the option to select LD 1964. 
  • You can write your testimony directly into the form, copy-and-paste your testimony into the form, or click the “CHOOSE FILE” button to attach a file of your drafted testimony.
  • Finally, you will then need to put your name and contact information into the form, check the “I am not a robot” box, and click the “submit/register” button.

If you need help submitting your testimony through the Maine Legislature’s website, please reach out to our Staff Writer Robby Lewis-Nash: email robbylewisnash [at] cascobay [dot] org or call (413) 695-3306. Robby looks forward to helping you make your voice heard. 

Bay temperatures rise as oxygen levels dip

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 long term dataset shows that water temperatures are on the rise in Casco Bay.


On average, water temperatures in Casco Bay are increasing at an approximate rate of 1°F every decade.*

“It’s alarming to see we’re going in the wrong direction,” said Staff Scientist Mike Doan. “There are so many ways that warmer water can impact the Bay. A primary concern is that warm water species are moving in and cold water species are moving out. Invasive green crabs, for example, thrive when the Bay is warmer. On top of species shifting, we are also looking at a system that is increasingly susceptible to nitrogen pollution. And that’s only the tip of the iceberg.”

When Mike says warmer waters make the Bay more susceptible to nitrogen pollution, he is thinking about how excess nitrogen can lead to lower levels of oxygen in the water. Nitrogen pollution comes from sources such as stormwater and wastewater treatment facilities. When excess nitrogen enters the Bay, it can spur the rapid growth of plant life and algae. When these plants inevitably decompose, they can consume so much of the oxygen in the water that aquatic animals like fish and shellfish struggle to breathe, and can even die.

On the whole, Casco Bay contains healthy levels of oxygen. However, water temperature and oxygen have an inverse relationship. Warm water holds less oxygen than cold water, and as water temperatures in the Bay rise, Mike has observed a corresponding decline in dissolved oxygen (a measure of how much oxygen is in the Bay).


On average, levels of dissolved oxygen are healthy in Casco Bay but are slowly decreasing at an approximate rate of 0.1 mg/L every decade.*

“There’s a very healthy amount of oxygen in the Bay right now, and the decline we’re observing is moving at a slow pace,” said Mike. “However, it’s important to keep our eye on this trend. As climate change causes the Bay to warm, oxygen levels will continue to decrease. With it, the impacts of nitrogen pollution and associated drops in oxygen will grow.”

Scientists up and down the New England coastline are reporting similar trends in temperature and dissolved oxygen. At Friends of Casco Bay, these trends are based on Mike’s analysis of a subset of 29 years of our seasonal sampling data. Specifically, Mike looked at data from three locations in the Bay that we access by boat near Fort Gorges, Clapboard Island, and in Broad Sound. At each of these sites we collect data at the water’s surface, and then every two meters down to the bottom of the Bay, to create a “profile” of the water column. Every one of these data points is included in Mike’s analysis, making him confident that these trends accurately reflect changing conditions in Casco Bay.


* The exact rates: water temperatures are rising at 0.99°F per decade and dissolved oxygen levels are decreasing at 0.091mg/L per decade.