Frequently Asked Questions

Once a body of water is identified, the Marine and Environmental Department will place signs at the public entrance(s) to alert the public. The State Department of Public Health maintains an active list of confirmed cyanobacteria blooms on its website.

Sign up for alerts and notifications.

Take a photo, document the location, and email the Plymouth Public Health or email the Plymouth Marine and Environmental Department.

Cyanobacteria Bloom Response Procedures (PDF)

• Advisories are not lifted until the water has been consistently clear for two weeks.
• Associations without public access are encouraged to post the Cyanobacteria Advisory Sign (PDF) in visible areas once a bloom is confirmed.
  • It is up to private pond associations to incorporate testing into their management plan, should they wish to do so.
• Only public bathing beaches are tested for e-coli bacteria per state health regulations, due to the large number of water bodies and expense of testing.
• Ponds with active blooms are identified and confirmed by visual observation for cyanobacteria by the state.

A confirmation of cyanobacteria bloom does not necessarily indicate it is toxic. Cyanobacteria may give off microcystin toxins. However, all cyanobacteria blooms are treated as potentially toxic to ensure public health.

• Advisories are not lifted until the water has been consistently clear for two weeks.
• Animals, birds, and fish can also be affected by high levels of toxin-producing cyanobacteria.
  • If your animal goes into the water, be sure to rinse them off thoroughly.
  • If your animal ingests water and shows signs of illness, contact your veterinarian.
• Skin irritation, stomach cramps, vomiting, nausea, diarrhea, fever, sore throat, headache, muscle and joint pain, blisters of the mouth, and liver damage.
• Swimmers in water containing cyanobacterial toxins may suffer allergic reactions, such as asthma, eye irritation, rashes, and blisters around the mouth and nose.

A bright green film that looks like "paint" in the water. May contain small white specs in the water column. Looks like an oil slick, green specks, pea green layer on the surface. View images (PDF) or visit Identifying cyanobacterial blooms and scums for more examples.

• Floating algae
• Has a musty odor
• It has a fuzzy appearance and is often green in color with blue highlights.

• Changes in Ph (phosphorous and/or nitrogen)
• Cyanobacteria are naturally occurring
• Failing cesspools/septic systems. Even non-failing systems contribute nutrients as septic systems only treat for bacteria, not phosphorus or nitrogen.
• Hot temperatures
• Increased rainfall
• Sediments in the bottom of ponds contain phosphorus from continuous loading from agriculture, septic systems, stormwater, rainfall, and fertilizers. Under low oxygen environments when temperatures increase can decrease the level of oxygen in the water column, thereby releasing the phosphorus from the sediment which feeds the cyanobacteria.
• Waterbodies with increased nutrients (phosphorus or nitrogen) will potentially feed the cyanobacteria into a bloom.

• Cyanobacterial Harmful Algal Blooms (CyanoHABs) in Water Bodies
• Harmful Algae Blooms in Freshwater Bodies
• Understanding Cyanobacteria in Our Ponds - Wildlands Trust Zoom Talk with Hilary Snook, senior scientist for the USEPA's New England Regional Laboratory.