I had knee replacements 10 years ago. The doctor says I have fluid on my knees. How? and what can I do about it?
Fluid on knee replacement : I had knee... - Kidney Disease
Fluid on knee replacement


What did the doctor say? Did he tell you what to do? I've had water on my knee and elbow in the past. They just drained it.
Inflamation or accumulation of uric acid can cause that, Also there are bursa in the knee that may have been ruptured bruise etc. That's the "cushioning" between the joints.

Those are questions to ask your doctor. Did you ask him when he told you this? Many causes which a trained physician can diagnose and give good responses. Wish you well.Blessings
It depends on the cause. It can be osteoarthritis, RA, infection, injury or even over-use (I probably forgot a few). Having the replacement probably isn't a factor, unless you need another.
How its treated depends on the cause. Get it drained then your Dr. will decide if you need antibiotics if the knee is hot, or maybe Cortisone injection for inflammation.
Did you injure the knee, did it hurt prior to developing fluid?
There are too many factors, only you and your PCP or Ortho can decide on the cause and treatment. I'd get it drained if it were me. I wouldn't wait for it to absorb.
Did your Dr. recommend alternating ice and heat every 15 min? That will help with pain if you have any.
Good luck.