Congestive heart failure is the primary cause of fluid on the lungs, reports Healthline. Other causes include sudden high blood pressure, lung damage from severe infection, inflammation of the pancreas and blood poisoning.
Fluid on the lungs makes the heart work harder than usual, which exerts pressure on the blood vessels in the lungs, causing the vessels to release fluid to the lungs, explains Healthline. The increased pressure can also come from factors such as severe trauma, high altitude exposure, drug overdose and near-drowning. This condition is more prevalent in people with heart problems, blood disorders and those with histories of lung diseases, such as tuberculosis.