Managing Cyanobacteria (Blue-Green Algae) at Milavec Reservoir

Caution Toxic Algea May be PresentThe Town of Frederick Parks and Open Space Department is monitoring and managing cyanobacteria at Milavec Reservoir through aeration, informational signs for recreational users, and working with upstream stakeholders and partners. Cyanobacteria blooms will happen, but through our efforts, we can manage the frequency and severity of annual blooms and inform recreational users of the potential impacts. 

When in doubt, it's best to keep out!

Water contact can cause illness

  • Keep kids out
  • No pets in water
  • Do not drink water
  • Avoid contact with algae
  • If exposed, shower immediately

Fishing Permitted: Rinse fish with clean water and properly dispose of guts
Boating Permitted: Avoid algae

 Cyanobacteria FAQs for Milavec Reservoir

What is Cynobacteria?

Cyanobacteria, also called blue-green algae, are microscopic organisms found naturally in all types of water. These single-celled organisms live in fresh, brackish (combined salt and fresh water), and marine water. These organisms use sunlight to make their own food. In warm, nutrient-rich (high in phosphorus and nitrogen) environments, cyanobacteria can multiply quickly, creating blooms that spread across the water’s surface. The blooms might become visible.

How are cyanobacteria blooms formed?

Cyanobacteria blooms form when cyanobacteria, which are normally found in the water, start to multiply very quickly. Blooms can form in warm, slow-moving waters that are high in nutrients from sources such as agricultural and turf fertilizer runoff, municipal wastewater effluent and septic system discharges. Cyanobacteria blooms need nutrients to survive. The blooms can form at any time, but most often form in summer or early fall.

What does a cyanobacteria bloom look like?

You might or might not be able to see cyanobacteria blooms. They sometimes stay below the water’s surface, they sometimes float to the surface. Blooms sometimes look like paint floating on the water’s surface. Some cyanobacteria blooms can look like foam, scum, or mats, particularly when the wind blows them toward a shoreline. The blooms can be blue, bright green, brown, or red. As cyanobacteria in a bloom die, the water may smell bad, similar to rotting plants. 

Why are some cyanbacteria blooms harmful?

Cyanobacteria blooms that harm people, animals, or the environment are called cyanobacteria harmful algal blooms. Harmful cyanobacteria blooms may affect people, animals, or the environment by: 

  • Blocking the sunlight that other organisms need to live. Cyanobacteria blooms can steal the oxygen and nutrients other organisms need to live.
  • Making toxins, called cyanotoxins. They can make people, their pets, and other animals sick.
  • You cannot tell if a bloom has toxins by looking at it.

How can people and animals come in contact with cyanobacteria and cyanotoxins in the environment?

People and animals can come in contact with cyanobacteria and cyanotoxins that are in the environment by:

  • Drinking water that comes from a lake or reservoir that has a cyanobacteria bloom.
  • Swimming or doing other recreational activities in or on waters that have cyanobacteria blooms

How do I protect myself, my family, and my pets from cyanobacteria blooms?

To protect yourself, your family, and your pets from cyanobacteria blooms:

  • Don’t swim, water ski, or boat in areas where the water is discolored or where you see foam, scum, or mats of algae on the water’s surface.
  • Do not allow children or pets to play in or drink scummy water.
  • If you do swim in water that might contain harmful cyanobacteria, rinse off with fresh water as soon as possible.
  • Don’t let pets swim in or drink from areas where the water is discolored or where you see foam, scum, or mats of cyanobacteria on the water’s surface.
  • If pets, especially dogs, swim in scummy water, rinse them off immediately. Do not let them lick the cyanobacteria off their fur.

Why do dogs get sick more often than people from cyanobacteria blooms?

Dogs will get in a body of water even if it looks or smells bad, including when it contains cyanobacteria. Dogs are also more likely to drink contaminated water. 

How are people or animals that have been exposed to cyanobacteria toxins treated?

If you or your pet comes in contact with a cyanobacteria, wash yourself and your pet thoroughly with fresh water.

  • If you or your pet swallow water from where there is a harmful algae bloom, call your doctor, a Poison Center, or a veterinarian.
  • Call a veterinarian if your animal shows any of the following symptoms of cyanobacteria poisoning: loss of appetite, loss of energy, vomiting, stumbling and falling, foaming at the mouth, diarrhea, convulsions, excessive drooling, tremors and seizures, or any other unexplained sickness after being in contact with water. 

How can you help reduce cyanobacteria blooms from forming?

To help reduce cyanobacteria from forming:

  • Use only the recommended amounts of fertilizers on your yard and gardens to reduce the amount that runs off  into the environment.
  • Properly maintain your household septic system.
  • Maintain a buffer of natural vegetation around ponds and lakes to filter incoming water.

Is there testing for cyanobacteria toxins?

Yes, but the testing is specialized and can only be done by a few laboratories. Scientists are working to develop toxin test kits for water resource managers and others.

What is the Town of Frederick doing to manage these blooms?

The Town is working towards a long-term solution for this important water quality issue, however, nutrient loads in Milavec Reservoir are extremely high, and will require significant investments of resources and time, in both upstream basin management and within the Reservoir body to alleviate frequent blooms. No management actions will permanently stop blooms, as cyanobacteria are natural to all waters and even with the best management efforts, can still bloom under the right conditions.

The Town installed a significant aeration system within the Reservoir, to increase water movement. This will not stop cyanobacteria blooms, but does manage their frequency and severity.

The Town is in discussions with upstream basin stakeholders to address nutrient loading issues.

The Town does not plan to treat the blooms, as the treatments include the use of pesticides and/or inorganic compounds, such as copper sulface, both of which can have significant unintended impacts on the aquatic ecosystem and fishery and can impact raw water irrigation systems, which the lake supplies around Town.

The Town is in the process of hiring a consultant to create a Master Plan for Frederick Recreation Area, which will also address long-term strategies to improve water quality for recreational use.

For more information on cyanobacteria: 


For information on the Town of Frederick's management of Milavec Reservoir:

Contact the Parks and Open Space Department - 720-382-5800