The New Hampshire Department of Environmental Services is warning those who visit lakes in Hollis and Hillsborough of a bloom of cyanobacteria that might produce health concerns.

The department released the advisory about blooms at Silver Lake in Hollis and Franklin Pierce Lake in Hillsborough on Monday.

The bacteria, which occur naturally in water, can cause a spectrum of health issues ranging from minor skin irritation to vomiting, seizures and liver and nervous system damage.

“Avoid contact with the water in areas experiencing elevated cyanobacteria cell conditions, typically where lake water has a surface scum, green streaks or blue-green flecks aggregating along the shore,” the New Hampshire Department of Environmental Services (NHDES) advises in a statement.

Pets should also be kept away from affected water, the agency says.

Both advisories will remain in effect until NHDES confirms that cell concentrations of the bloom have subsided.

At Silver Lake, the park’s beach and boat launch both tested positive for high levels of the bacteria.

The cyanobacteria bloom observed on June 8 appeared orange, yellow and blue-green. Follow-up samples were collected June 10.

At Franklin Pierce Lake in Hillsborough, a surface scum accumulating along the shoreline that appeared yellow and blue-green in color. Samples collected from the beach area exceeded the state threshold of 70,000 cells/ml of cyanobacteria. As a result, NHDES issued a cyanobacteria advisory for those who swim at the beach and use the lake for recreation.

It is also advised to look out for accumulations in other areas of the lake and avoid contact.

In a news release, NHDES said both advisories are based on a toxin evaluation and are intended as precautionary measures for short term exposure.

Cyanobacteria are bacteria that grow in colonies to form surface water “blooms,” usually blue-green in color and consisting of thousands and even millions of individual cells, according to DES.

The bacteria occur naturally in most New Hampshire lakes, usually in relatively low numbers.

Cyanobacteria can increase as lake nutrients increase. And some cyanobacteria produce toxins that can adversely affect humans, domestic animals and livestock.