At least five sailors serving aboard the USS Nimitz aircraft carrier have reported health issues that “may have been related” to a potable water supply discovered this month to have been contaminated by jet fuel, the U.S. Navy said Thursday. The acknowledgement comes roughly two weeks after the service first detected fuel “traces” in the water supply, and just days after it determined that further tests continued to show signs of leakage. The affected sailors “are being closely monitored by health officials,” according to 3rd Fleet spokesman Cmdr. Sean Robertson. Four have been cleared, while one continued to suffer from acid reflux as of Thursday. The source of the contamination has been identified and isolated, Robertson added, according to the Navy Times. The carrier’s crew is drawing safe water from San Diego, moored at its homeport of Naval Air Station North Island after an earlier planned deployment was scuttled by the leakage issue.