There are a number of reasons why the lung can become congested with fluid. Among those are chronic kidney failure, chronic kidney disease without frank failure but with excessive protein loss, called nephrotic syndrome,
congestiveHeart failure
Left-sided heart failure
Right-sided heart failure heart disease, disease of a heart valve, fat emboli (
clotsBlood clots) in association with long bone fractures, IV salt and/or water overload, high altitude, acute infection such as pneumonia with or without fever, and chronic infection with tuberculosis (TB) being a prime example. And, there are other less common causes.
The suspicion of fluid on physical exam should be followed by reevaluation of kidney function and a chest x-ray. With this information it should be possible to decide-upon the most likely cause(s) and initiate appropriate therapy.