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Key Water Reporter Issues
Nuisance Algal Blooms
Algae are a natural part of marine ecosystems, but too much nitrogen in Casco Bay—from fertilizers, pet waste, sewage, and air pollution—can fuel excessive growth. When algae grow out of balance, they can form dense mats that smother clam flats, cloud the water, lower oxygen levels, and create stressful conditions for marine animals and plants.
Algal blooms also occur in freshwater, often driven by excess phosphorus. While our current science and advocacy work focuses on marine algae in Casco Bay, Water Reporters are welcome to document freshwater blooms as well.
What to Look For
Algae in the marine environment may appear as slimy mats or green fuzz, often without clear roots or structure. It can float in the water or cover rocks, mud, and other shoreline surfaces.
We’re looking for photos of algae and photos showing little to no algae. Documenting both presence and absence helps us understand when and where nuisance algal blooms are forming—and where conditions remain healthy. Over time, these observations help us spot patterns, identify problem areas, and respond more effectively.
Below are examples of nuisance algal blooms seen around Casco Bay.
Tap or click any image to open the full gallery.
How & Where to Track Algal Blooms
Choose a location to monitor weekly or biweekly.
Use our interactive map to find a suggested site, or pick your own. Let us know if you’d like to formally commit to a site!Visit during low tide.
Aim to take your photos between an hour before and after low tide. Check tide times here or on a tide app.Take two types of photos:
A wide shot with a landmark for consistency
A close-up if algae are present
Post to Water Reporter. Include these notes in your post:
Presence or absence of algae
Site name
Changes since your last visit (more, less, same)
Where algae is growing (low, mid, or high intertidal)
Adjust the date and time if you are posting later
Use the interactive map to find locations we’re keeping an eye on.
How You Can Help
Reduce Nuisance Algal Blooms
- Stop or minimize use of fertilizers on your lawn or garden.
- Pick up pet waste and dispose of it properly.
- Keep your car tuned up to reduce pollution from tailpipes.
- Empty your boat’s holding tank at a pumpout facility or use our Pumpout Service to keep sewage out of the Bay.
- Maintain your septic system.
- Burn less oil, wood, and coal to reduce pollution from smokestacks.
- Help us track algae as a Water Reporter!
Learn More About Algae
Learn the difference between algae and other coastal plants.
Learn about a harmful brown-colored algae
