Seven lakes in one of South Jersey’s most rural counties have been swarmed as of this week by harmful algae blooms, according to officials. It continues a toxic trend in the Garden State this year, beginning in June with the closure of the state’s largest freshwater lake, Hopatcong in Sussex County.

On Wednesday, the Salem County Department of Health and Human Services issued a public advisory warning that people and their pets should not come into contact with water in the lakes connected to the Salem River. Sampling by the New Jersey Department of Environmental Protection confirmed the presence of toxic blue-green algae blooms.

The notice urged the public to "avoid swimming, water sports and activities including: fishing, kayaking, canoeing, and recreational boating. Fish that are caught in these waters should not be eaten. The public is also advised that pets and livestock should not be allowed to drink or come into contact with these waters.”

County officials named Memorial Lake in Woodstown, Daretown Lake in Daretown, Elmer Lake in Elmer, and East Lake, Avis Mill Pond, and Slabtown Lakes, all in Pilesgrove. They also named all parts of the Salem River — a 34-mile-long tributary of the Delaware River — between Daretown and Memorial Lakes as affected.

“We’re trying to be proactive," said Stacy Pennington, the county administrator. “They’re typically not swimming lakes, but you will find people fishing off bridges. Our big concern is for farmers. We want to make sure no cattle go near the water. And we don’t want pets in there.”

Blue-green algae, a yearly occurrence at some lakes and ponds, has emerged as a growing scourge, and took on greater notoriety this year following the deaths of four dogs in North Carolina and Georgia after swimming in a pond loaded with it.

Blue-green algae is not truly an algae, but the common name for a type of cyanobacteria. The blooms appear as a thick coating on the water, usually in late summer or early fall. Not all blooms are cyanobacteria; some are common green algae, which are not toxic.

Cyanobacteria can produce toxins harmful to people, pets, and livestock. Exposure to cyanobacteria can lead to rashes, allergylike reactions, flulike symptoms, gastroenteritis, respiratory irritation, and eye irritation, according to the county notice. Symptoms can occur in sensitive individuals even at low levels.

The cyanobacteria 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.

Salem County is one of the most agriculturally significant counties in New Jersey. Of the state’s 21 counties, it has the largest number of state preserved farmland acres with 37,838 acres on 334 farms.

According to the 2017 U.S. Census of Agriculture, the most recent, there are an estimated 781 farms totaling 98,239 acres in Salem County.

Blue-green algae cases have been confirmed in other South Jersey counties. As of this week, Sylvan Lake in Burlington Township, Amico Island Pond in Delran, and Pemberton Lake in Pemberton, all in Burlington County, had cases of confirmed harmful algal blooms. Dramesi Lake Park in Gloucester Township, Camden County, also had a confirmed case. According to a state Department of Environmental Protection database, there were 28 algae blooms confirmed as of this week.

The New Jersey Sierra Club blamed the spread of blooms this year on officials’ failure to take action at a time when summers are getting warmer, and blooms are more likely.

“This is a record year for algae blooms and closed lakes,” Jeff Tittel, director of the Sierra Club, said in a statement. He called for the establishment of standards that limit pollutants.

For more information on algae blooms, New Jersey residents can visit state.nj.us/dep/hab/. To report a suspected harmful bloom, residents can call the NJDEP Hotline at 1-877-WARNDEP (877-927-6337).