Scientists say they’ve discovered a new organ — possibly the human body’s largest — and it was hiding in plain sight, according to a new study.

The so-called interstitium is an interconnected system of tiny fluid-filled cavities throughout the entire body that acts as a “highway” for our internal water supply, study co-author Dr. Neil Theise told LiveScience.com.

The findings were published Tuesday in the journal Scientific Reports.

The human body is 60 percent water, and while two-thirds of that liquid remains inside cells, the remaining water — called interstitial fluid — is free to move throughout cavities inside the body.

Scientists had not previously shown that there was a unified system for moving that water, because they “didn’t know what they were looking at,” Theise told LiveScience.com.

The interstitium exists within connective tissue, beneath the skin and surrounding several other organs and could be considered the body’s largest organ, researchers said.

But a greater consensus among the scientific community is needed before the interstitium can be officially called an organ, according to Theise, a professor of pathology at New York University Langone School of Medicine.

Researchers previously thought the space between flesh and organs was made up of solid collagen — a protein — but Theise’s research reportedly shows that space is actually a scaffolding of collagen that’s filled with water.

Thinly slicing tissue to put it under a microscope destroys the collagen structure of the interstitium, so it wasn’t until researchers used a new mode of viewing living tissue on the microscopic level, called “probe-based confocal laser endomicroscopy,” that they were able to detect the interstitium.

The pseudo-organ could act as “shock absorbers” for internal organs, Theise told NewScientist.com.

But it may also explain how cancer cells are able to spread throughout the body — a process that has remained opaque for researchers, the study found.