If you have fluid on the knee will it go away on its own?

Effusion: Unclear. Fluid on the knee (effusion) can come from a number of causes and some times it will go away without treatment other times it won't. The most common causes of fluid in the knee are an acute traumatic injury, meniscal tears and forms of arthritis or cartilage lesions. Effusions from trauma can resolve on their own provided that they have not caused a meniscal tear or cartilage injury.