What Happens in the Lake Doesn't Stay in the Lake
Surface water — lakes, rivers, and reservoirs — is the source of drinking water for millions of Americans. The health of our watersheds directly affects what comes out of our taps. From harmful algal blooms to microplastics, protecting our lakes means protecting our families.
Harmful Algal Blooms (HABs)
Harmful algal blooms are overgrowths of cyanobacteria (blue-green algae) that can produce toxins harmful to humans, pets, and wildlife. They thrive in warm, nutrient-rich water — and are increasing with climate change and agricultural runoff.
How to Spot a Harmful Bloom
Green, blue, or brown discoloration
Water looks like pea soup, spilled paint, or has a green sheen on the surface.
Scum or foam on the surface
A visible layer of algae, foam, or scum floating on the water.
Musty or earthy odor
A strong, unpleasant smell coming from the water, especially near shore.
Dead fish or wildlife
Fish kills or sick animals near the water can indicate toxic bloom conditions.
If You See a Bloom
- ⚠Do not swim, wade, or allow pets in the water
- ⚠Do not drink or cook with the water — boiling does NOT make it safe
- ⚠Do not eat fish caught from the affected area
- ⚠Rinse off immediately if you or your pet contact the water
- ⚠Report the bloom to your state environmental agency or health department
- ⚠Keep children and pets away from shorelines with visible blooms
Report blooms to your state environmental agency or health department. Many states have HAB hotlines and online reporting tools.
What an Algal Bloom Can Look Like
Real photographic examples of cyanobacterial blooms from the U.S. EPA. These photos show common visual signs -- surface discoloration, paint-like scum, and reduced transparency -- that can help you recognize a possible bloom before official testing confirms it.
Pea-soup surface bloom with shoreline scum
A classic planktonic cyanobacterial bloom. The water surface is covered in opaque, bright green material that looks like pea soup or spilled green paint. Notice the concentrated white-yellow scum where the bloom meets the shoreline -- this is where wind has pushed material to accumulate.
Location: Sudbury River, Massachusetts
Photo: Susan Flint
Source: U.S. EPA
Bright green paint-like bloom along shore
A distinct line of bright green cyanobacteria along the shore, contrasting sharply with the deeper, clearer water. This "paint-like" edge is a common visual sign. The bloom is concentrated where wind and currents push surface material toward the bank.
Location: Lake Attitash, Merrimac, Massachusetts
Photo: Nancy Leland
Source: U.S. EPA
Large-scale bloom -- aerial contrast view
An aerial view showing the stark contrast between a bloom-affected water body (opaque olive-green) and clear water (deep blue). This illustrates how a bloom can cover a large area and dramatically reduce water transparency. The green tint and reduced clarity are key visual signs.
Location: Monponsett Pond, Halifax, Massachusetts
Photo: Edward Broderick
Source: U.S. EPA
Benthic (bottom-growing) mats
Not all cyanobacterial blooms float on the surface. Benthic blooms grow on the bottom of lakes and rivers, attached to rocks, sand, or plants. They can look like brown or dark-green algae coating underwater surfaces. Pieces can detach and float to the surface, accumulating along shorelines as loose mats.
See benthic mat photos -- Oregon Health Authority GalleryAlgae vs. Cyanobacteria
Not all algal blooms are toxic, and not all toxic blooms are cyanobacteria. Cyanobacteria(also called blue-green algae) are bacteria, not true algae -- but they can look similar. True algal blooms (green algae, diatoms) are common and usually harmless. Cyanobacterial blooms are the primary concern for toxin production. Visual identification alone cannot distinguish toxic from non-toxic blooms -- only laboratory testing can confirm whether toxins are present.
Important: Photos show possible signs, not proof of toxins. Blooms can be harmful without looking like these photos, and toxins can be present before or after a visible bloom. Avoid contact with suspicious water; keep pets away; check current local advisories and report suspected blooms to the appropriate local authority. Only testing can confirm toxins.
Microplastics in Surface Water
Microplastics and nanoplastics are now found in nearly all surface water — from remote mountain lakes to urban rivers. They enter waterways through plastic waste, synthetic textile fibers, tire dust, and wastewater discharges.
The Scale
Studies estimate that 24 trillion pieces of microplastic are in the world's oceans — and freshwater systems carry comparable concentrations. Lake water can contain more plastic particles than ocean water in some areas.
The Tap Water Link
Microplastics from surface water can pass through some drinking water treatment plants. A 2024 Columbia University study found hundreds of thousands of plastic particles per liter in bottled water.
What You Can Do
Reverse osmosis is expected to remove most nanoplastics based on size exclusion. Reducing single-use plastic and supporting plastic reduction policies addresses the source.
As of September 2026, there is no regulatory standard or certified consumer test for nanoplastics in drinking water. This is an emerging concern we are actively tracking.
Source Water Protection: The Watershed-Tap Connection
What happens in the watershed ends up in the tap. Protecting source water — the lakes, rivers, and aquifers that feed our water systems — is the most cost-effective way to ensure clean drinking water. Treatment can remove contaminants, but prevention keeps them out in the first place.
The Multi-Barrier Approach
The most effective water protection strategy uses multiple barriers: source water protection → water treatment → distribution system integrity → point-of-use filtration. Each layer catches what the previous one misses.
Watershed Stewardship Actions
You don't need to be a scientist to protect your watershed. These six actions make a measurable difference.
Reduce fertilizer use
Excess nitrogen and phosphorus from lawns and gardens fuel algal blooms. Use slow-release fertilizer and follow application rates.
Maintain your septic system
Pump every 3–5 years. Failing septic systems leach bacteria and nitrates into groundwater and surface water.
Plant a buffer zone
Trees, shrubs, and native grasses along shorelines filter runoff, stabilize banks, and provide habitat.
Pick up pet waste
Pet waste contains bacteria and nutrients that wash into storm drains and waterways during rain.
Dispose of chemicals properly
Never pour paint, oil, medications, or cleaning products down drains or storm sewers. Use hazardous waste collection.
Support local water protection
Join your watershed association, attend local water board meetings, and advocate for source water protection.
Protect your water from source to tap
Join the movement for clean water — for our lakes, our families, and our future.
Take Action