Blue-green algae, a yearly occurrence at some lakes and ponds, has emerged as a growing scourge this summer after an outbreak forced New Jersey to shut down beaches at its largest freshwater lake.

On top of that, four dogs died this month in North Carolina and Georgia after swimming in a pond loaded with it.

Should you be afraid? Here are answers to some basic questions about the bacteria and its risks.

What is blue-green algae?

Blue-green algae is the common name for a type of cyanobacteria, though these bacteria aren’t truly a form of algae. Cyanobacteria can produce toxins harmful to people, pets, and livestock. They mostly grow in freshwater lakes and streams, but they are also found in marine waters, such as estuaries. When blue-green algae grow excessively, it’s called a bloom. Usually, the trigger is a combination of sunlight, high temperatures, and nutrients, generally from lawn and farm fertilizers.

The blooms appear as a thick coating on the water, usually in late summer or early fall. But not all blooms are cyanobacteria. Some are common green algae, which are not toxic.

After testing in June, the New Jersey Department of Environmental Protection confirmed that a mat of algae on Lake Hopatcong in Sussex County fit the definition of a harmful algal bloom (HAB). Beaches at the state’s largest lake were closed. Just this week, the DEP lifted an advisory against swimming in the lake. In all, the state has confirmed 16 locations this summer where harmful algal blooms were present, all in central or northern New Jersey.

Harmful blooms haven’t been reported at Southeastern Pennsylvania swimming beaches this summer, though the Army Corps of Engineers did issue an advisory for popular Blue Marsh Lake in Berks County a few weeks ago when algal blooms were found. Stephen Rochette, a corps spokesperson, said the blooms never rose to levels that posed a concern for toxins.

How can I keep my pets safe?

First, regardless of whether algae is present, many waterways are already “impaired” in the Philadelphia region, meaning they have some degree of pollution. The waterway might get flows of road runoff containing gas and oil, and stormwater runoff that contains chemicals and untreated sewage. Drinking the water, which can contain high levels of fecal and other bacteria, can make people — and pets — sick.

If you wouldn’t swim in it, it’s a good bet it’s not good for your dog.

According to the U.S. Environmental Protection Agency, you should not let your dog drink or swim in water if it looks slimy, or if there is foam or scum on the surface. If the color is weird, that’s another indicator that something is wrong.

Cyanobacteria can vary in color. Aside from the familiar blue-green, harmful blooms may be blue, bright green, brown, or red. They may resemble paint floating on the surface.

A strong, even nauseating, odor is another indicator. If the water stinks, it’s probably not safe.

What can happen to me if I’m exposed?

The toxins in harmful algal blooms can sicken people who drink the water, or just accidentally swallow it while swimming, boating, or fishing.

Some of the symptoms are rashes, stomach or liver illness, respiratory issues, or neurological problems.

If you swallow water from a location that may have a harmful algal bloom, call your doctor or a poison center.

What if I think my dog or pet has been exposed?

Symptoms of a toxic effect might not be immediately apparent and can take days to appear. Some of the symptoms include diarrhea, vomiting, weakness, staggering, drooling, difficulty breathing, or convulsions.

If you think your dog has been swimming in a pond or lake with cyanobacteria, rinse the pooch immediately with clean, fresh water. You should wear protective gloves while bathing your dog.

Take the dog to the vet immediately if you see any symptoms arise.

What if I spot or suspect a harmful algal bloom?

It’s best to report it to your state environmental agency.

In New Jersey, the DEP is telling residents to report through an online tool or call 1-877-WARNDEP (1-877-927-6337).

If blue-green algae isn’t new, why am I hearing so much about it now?

It appears to be proliferating. The Environmental Working Group examined filings by the EPA in its National Lakes Assessment, conducted every five years. EWG also looked at data filed by 14 states that monitor for microcystins, a class of toxins produced by blue-green algae.

In both 2007 and 2012, the most recent data available from the EPA, testing found microcystins in water bodies in all of the contiguous 48 states. But the EPA showed that there was a near 10% increase in that period. The 2017 survey results are not yet public.

The EPA has said microcystins and some other cyanotoxins are candidates to be regulated under the Safe Drinking Water Act. But the EWG said establishing standards could take years.

Is climate change a factor?

The conditions that mark climate change also can promote blue-green algae. EWG says recent outbreaks of blue-green algae are starting earlier in the year and lasting longer.

The group cites increasing rainfall and rising temperatures as contributing to the growth of blooms. More rainfall means more pollution and runoff ends up in streams, lakes, creeks, and rivers.

The New Jersey Conservation Foundation said increased storm runoff could be fueling some of the nutrients cyanobacteria need to flourish. Municipal storm systems can’t handle the additional water, so the systems overflow, allowing runoff to go directly into streams and waterways.

The foundation said residents can help by not using chemical fertilizers on lawns and gardens, maintaining their septic systems, planting native trees or shrubs around waterway edges to filter out contaminants, building rain gardens, installing rain barrels, and properly disposing of pet waste. Leaving the waste to be washed away by the next rain means it goes into the nearest waterway.

Isn’t blue-green algae sold as a dietary supplement?

Yes, but it’s not the same as what’s plaguing waterways. According to WebMD: “Some blue-green algae products are grown under controlled conditions. Others are grown in a natural setting, where they are more likely to be contaminated by bacteria, liver poisons (microcystins) produced by certain bacteria, and heavy metals. Choose only products that have been tested and found free of these contaminants. You may have been told that blue-green algae are an excellent source of protein. But, in reality, blue-green algae are no better than meat or milk as a protein source and cost about 30 times as much per gram.”