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What is a Warning ?
Warnings are issued lake-wide when cyanobacteria cell counts exceed the recreational health threshold of 70,000 cells/mL. Surface blooms can rapidly change and accumulate in various locations around a waterbody. Please continue to monitor shorelines for changing conditions. NHDES advises lake users to avoid contact with the water in areas experiencing blooms. Pets and livestock should also be kept out of the water.
When a warning is issued, resampling is performed weekly until the bloom subsides. Warnings are issued from May 15 through October 15. Warnings are not based on toxin evaluation but occur at cyanobacteria cell count densities when toxin production may be likely and are intended as a precautionary measure for short term exposure to cyanotoxins.
Blooms are dynamic. Always perform a self-risk assessment of the water, looking for discoloration or unusual growth prior to recreating. If you see cyanobacteria develop after a warning has been closed, please report it.
What is an Alert?
Alerts are issued 1) based on a photo before NHDES can analyze a sample; 2) when the cyanobacteria density is approaching the recreational health threshold but does not yet exceed it; or 3) if a bloom was reported but may have passed by the time a sample was reviewed but could reoccur. Alerts are intended to serve as statements to be on the watch for a potential cyanobacteria bloom. Waterbody users should avoid contact with bloom material and keep pets and livestock out of the water. Sometimes alerts become warnings, and sometimes they pass. Alerts remain active for a week. Resampling only occurs if further bloom reports are submitted. Alerts are issued year-round as needed.
Cyanobacteria Basics:
Cyanobacteria are natural components of water bodies worldwide, though blooms and surface scums may form when excess nutrients are available to the water. Some cyanobacteria produce toxins that are stored in the cells and released into the water when the cells die. Toxins can cause both acute and chronic health effects that vary in severity. Acute health effects include irritation of the skin and mucous membranes, tingling, numbness, nausea, vomiting, seizures, and diarrhea. Chronic effects may include liver and central nervous system damage. Be cautious of lake water that has a surface scum, changes colors, or appears to have green streaks or blue-green flecks aggregating along the shore.
If a person or animal is sick from a potential cyanobacteria exposure, please seek medical attention. Inform your physician or veterinarian that you or your pet may have been exposed to toxic cyanobacteria via recreation. Please also fill out our Illness Report Form, (updated spring 2024) and see the CDC guidance for Health Care Providers and Veterinarians.
Questions?
For more information, see the NHDES Harmful Algal Bloom Webpage and our Frequently Asked Questions (updated spring 2024). Sign up for waterbody- specific emails to receive more details for that specific waterbody (warning or alert issuance, resampling results and warning removal).
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