New Jersey’s largest public school system has shut off the drinking fountains at some of its schools after tests found elevated lead levels in the water there, officials said Wednesday.

The state Department of Environmental Protection (DEP) and Newark Public Schools made the announcement in a joint news release, saying annual testing showed elevated levels of the contaminant in water collected from select taps in 30 of the district’s school buildings.

Roughly 300 samples were collected from those schools, the state DEP said, and 59 showed levels that were above a federally mandated threshold of 15 parts per billion. The Environmental Protection Agency now requires further action, including testing, monitoring and remediation.

The water fountains will remain off until more testing is performed.

Being exposed to lead can trigger a variety of health problems, according to the Centers for Disease Control and Prevention, and children who have the element in their bodies may experience developmental delays and issues with their hearing, speech and learning.

But the severity of any adverse health effects depends on how much lead builds up in a person’s body over time, according to a New Jersey Department of Health fact sheet on lead in water.

“Typically, drinking water alone has not been associated with elevated blood lead levels,” the fact sheet states. “Combined with other sources, however, the amount of lead from drinking water may be enough to increase the chances of harmful health effects in sensitive individuals, such as infants and children.”

Newark Public Schools has 66 schools and more than 35,000 students, according to its website.

The system says it is sending out letters to parents that inform them of the test results, outline the steps being taken and assure that students will still have safe food and water while at school.

In a message on its website, the school system said it has begun placing bottled water in the affected schools “as a precautionary measure.” It has also posted signs in bathrooms that instruct people not to drink from the faucets, and supplied alternative water for cooking.

The state DEP said that the Newark Water Department, the school’s supplier, does not have lead in its water. The agency said that most cases of elevated lead levels in water involve the element leaching in through lead pipes, or other fixtures and solders that contain lead.