REVIEW 1992 TO 2021
STATE OF THE BAY REPORTS
STATE OF CASCO BAY
6th Edition
Every five years, Casco Bay Estuary Partnership gathers and analyzes the best available data on water quality, land use, habitat coverage, and other key indicators to assess the Bay’s health. We present the findings in State of the Bay reports that share vital information used by stakeholders and decision-makers to protect and enhance the condition of the Bay.
State of Casco Bay, 6th Edition marks nearly thirty years of science and monitoring efforts that have greatly improved understanding of the Bay and documented three decades of change. It presents findings for nineteen indicators organized in three groups: Drivers & Stressors, Condition of the Bay, and Human Connections. Together, these interrelated indicators provide a framework for understanding the causes and outcomes of change in the Bay and for implementing effective solutions.
The entire report may be viewed and downloaded as a printer-friendly PDF file. Individual chapters may be viewed online by clicking on chapter titles in the Table of Contents below. Buttons at the bottom of each chapter’s web page provide options to view/download a pdf of that chapter, see supplementary information, or go to the data repository.
The keynote speech presented by CBEP Director Curtis Bohlen at the November 2022 Maine Stormwater Conference is available here.
Introduction
DRIVERS & STRESSORS
What’s Affecting the Bay?
A. Population & Land Use
New Suburban Construction Eats into Forests and Agricultural Lands
Population of Casco Bay Watershed Grew Nearly 10 Percent in 18 Years
B. Stormwater
Stormwater Runoff Degrades Water Quality in Urban Streams
Salt from Winter Deicing Products Poses a Threat to Urban and Suburban Waters
C. Combined Sewer Overflows
Community Investments Have Reduced Pollution from Combined Sewer Overflows (CSOs)
Discharges from CSOs Dropped by Eighty Percent Over Two Decades
D. Inland Water Quality
Most Lakes and Streams Meet Water Quality Standards
Urban Waters More Likely to Have Poor Water Quality
E. Climate Change
Maine’s Climate Has Been Changing for Decades
Winters Have Become Warmer, and Rainfall More Intense, as Sea Level Has Risen and High Tide Flooding Increased
F. Invasive Species
Invasive Species Persist in a Warming Casco Bay
Tunicates Are Especially Abundant and May Displace Other Species
CONDITION OF THE BAY
How Is the Bay Doing?
G. Bay Water Quality
Bay Water Temperatures Increased 1.6°C (3°F) in Three Decades
Inshore Waters May Be More Vulnerable to Water Quality Problems
H. Nutrients
Nutrient Pollution Puts Bay Water Quality at Risk
Community Efforts to Protect Water Quality and the Bay’s Natural Resilience Have Prevented Widespread Impacts
I. Aquatic Connectivity
Sea-Run Fish Regaining Access to the Presumpscot Watershed
Relic Dams Block Fish from Swimming Up Royal River, Stroudwater River, and Some Coastal Streams
J. Eelgrass
Eelgrass Increased from 2013 to 2018 but Remains Below Historical Abundance
Beds in Freeport and Brunswick Rebounded Through Natural Propagation
K. Coastal Acidification
Coastal Acidification Varies Seasonally, Daily, and Among Locations in Casco Bay
Scientists Are Investigating Local Patterns and Causes of Acidification
L. Swimming Beaches & Shellfish Beds
Elevated Bacteria Levels Occur at Some Monitored Locations
High Bacteria Numbers More Common Downstream of Urban and Suburban Areas
M. Toxics
Persistent Toxics Have Declined Over Past 30 Years
Uncertainties Remain about Impact of Novel Contaminants
HUMAN CONNECTIONS
What’s Being Done?
N. Conserved Lands
Fourteen Percent of Land in Casco Bay’s Watershed Has Been Permanently Conserved
In Coastal Communities, Conservation Land Approaches Ten Percent
O. Coastal Habitats
Casco Bay Has 16,655 Acres of Tidal Habitats
Over a Hundred Acres of Tidal Marshes Restored Through Culvert Replacement
P. Economics
Bay Has $700 Million Economic Impact
Tourism and Marine Resources Are Key Sectors of Coastal Economy
Q. Education
Place-Based Education Engages Thousands of K-12 Students Around Casco Bay
Schools and Nonprofits Collaborate to Provide Environmental Education
R. Stewardship
Volunteers Donate More than 17,000 Hours to Stewardship of Casco Bay
Organizations Engage Volunteers in Wide Range of Roles
S. Climate Preparedness
Municipal and Community Leaders Take Action Toward Climate Resilience
Many Paths to Community Resilience and Adaptation in Casco Bay
Supplementary Materials
Data Repository
Selected data and data analysis code for certain Indicators are available for review at GitHub. A full archive of data and all analysis steps is available at GitHub Details.Interactive Map
Explore an interactive map of much of the data featured in the State of Casco Bay, 6th Edition.
Regional Highlights
See highlights of State of Casco Bay findings pertaining to each region:
- Eastern Bay: New Meadows; Harpswell Sound/Quahog; Maquoit & Middle Bays
- Inner Bay: Harraseeket River; Broad Cove/Cumberland & Falmouth Foresides; Islands
- Presumpscot: Lower Presumpscot
- Royal: Royal & Cousins Rivers
- South Bay: Fore River & Back Cove; Southern Bay
- Upper Watershed: Sebago/Upper Presumpscot
If you would like to receive a printed State of Casco Bay report, send an email request to cbep@maine.edu.
This document has been funded by the U.S. Environmental Protection Agency under Cooperative Agreements #CE00A00348-0 and #CE00A00662-0 with the University of Southern Maine.
Suggested citation: Casco Bay Estuary Partnership. State of Casco Bay, 6th Edition (2021).
