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Cooling Lagoons

North Anna Power Station uses water from Lake Anna to condense steam back to water inside the station. The water is returned to the lake slightly warmer than when it was taken. The discharged water cools in a series of private cooling lagoons, known as the Waste Heat Treatment Facility (WHTF).

When North Anna is in full operation, approximately 2,000,000 gallons of water pass through the station per minute.


Lake Anna was developed to provide cooling water for North Anna and is 17 miles long, 1 1/2 miles wide, and offers 200 miles of shoreline. Download a brochure on Lake Anna.

Harmful Algae Blooms

Algae are naturally-occurring microscopic organisms that are found in fresh and salt waters of Virginia and around the world. Many are beneficial because they are major producers of oxygen and food for many of the animals that live in these waters. Algae blooms can occur when warm water and nutrients combine to make conditions favorable for algae growth. Excessive rain typically results in nutrient-runoff from the land that can trigger algae blooms in natural waters.

Most algae species are harmless; however, some species may produce irritating compounds or toxins. These toxins can cause skin rash and gastrointestinal illnesses, such as upset stomach, nausea, vomiting and diarrhea in humans, particularly children, and pets.

Discolored water or scums that are green or blueish-green should be avoided, as they are more likely to contain toxins. Scums are more likely to occur in coves, shallow areas, or along the shoreline.

Dominion Energy, in collaboration with the Virginia Department of Health (VDH), has a sampling plan to evaluate reports of suspected Harmful Algae Blooms in the WHTF. When a suspected HAB is reported or observed, the company's Corporate Biology group gathers samples and tests them based on VDH's sampling protocol. Dominion Energy Corporate Biology staff has been added to VDH's list of recipients of Harmful Algae Bloom reports in Virginia.

The company and VDH advise reporting suspected HABs on Lake Anna and in the WHTF by filling out the Harmful Algae Bloom Online Form. To report health effects only, call the VDH hotline at 888-238-6154.

As a result of testing and evaluation performed in accordance with current Virginia Department of Health guidelines, all “no-swimming” advisories for the Waste Heat Treatment Facility have been lifted as of July 25, 2019. Recreational users of the Waste Heat Treatment Facility are advised to remain on alert for all algae blooms. If water is discolored, has an odor, or if there appears to be a film on the water surface, swimming is not advised for humans or pets.

WHTF HAB Monitoring Map

To report health effects, contact the HAB Hotline: 888-238-6154

To report suspected HABs, fill out the Harmful Algae Bloom Online Form (do not use this form to report health effects).

To prevent illness, people should:

  • Avoid contact with any area of the lake where there is scum or an advisory sign is posted.
  • Do not allow children or pets to drink from natural bodies of water.
  • Keep children and pets out of the areas experiencing a harmful algae bloom and quickly wash them off with fresh water after coming into contact with algae.
  • If you or your animals experience symptoms after swimming in or near an algal bloom, seek medical/veterinarian care.
  • If you suspect you experienced health-related effects following exposure to a bloom, contact the Virginia Harmful Algal Bloom Hotline at 888-238-6154.
  • To learn more about harmful algae blooms, visit

Lake Anna Conditions

Lake Anna's water level and temperature readings are updated once each weekday. The temperature is measured in water being drawn directly from the main lake into the station's intake. The lake level is based on feet above sea level as measured at the main dam.
Date Temperature (deg. F) Lake Level (ft.)
7/12/2024 87 249.3

WHTF Water Temperatures

Discharge Water

By design, the temperature of the discharge water is typically 14 degrees warmer than the intake water (displayed above). Intake temperatures can fluctuate with seasons or weather conditions. The data below is posted daily, M-F, as a public service.

Date Time Discharge Temp. (°F)
7/11/2024 6:15 a.m. 103°
7/10/2024 6:50 a.m. 103.6°
7/9/2024 6:33 a.m. 102.9°

Lagoons 2 & 3

As the discharge water flows to lagoons 2 and 3, it gradually cools, and is eventually returned to the main lake. The period of primary recreational use in the lagoons (May 1 – October 31) is typically the period with the highest water temperatures and the greatest recreational use. Individuals choosing to use the lagoons for recreational purposes should consider these temperatures in relation to health risk information contained on the Virginia Department of Health's website. 

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