For many years, that anguished winter was what made Campbell’s party famous, but for modern-day scientists of Antarctica, it’s a stray note in Campbell’s notebook that makes his journey worth remembering. Tucked away in the explorer’s 105-year-old journal is a passing mention of liquid water on Antarctica, a phenomenon that hydrologists are just now beginning to understand.

The first-ever hydrological survey of Antarctica has just been completed, and it found nearly 700 streams, ponds, and waterfalls, a sprawling and active meltwater drainage system never previously documented. The system appears to cover the entire continent, carrying water across both grounded ice and the floating ice shelves which surround its coast.

Its scale rivals anything found on the more temperate parts of the planet. Ponds can grow to be gargantuan—50 miles long—fed by streams carrying as much water as the Potomac or the Hudson. One stream system drains water from the heights of the Trans-Antarctic Mountains, more than 4,000 feet above sea level. Another ferries meltwater more than 75 miles, from glaciers on the land-surface of the continent to a large pond in the Ross Ice Shelf.

The survey was announced Wednesday in two papers in the journal Nature. It brought together decades of aerial and satellite photography of Antarctica with some of the earliest documented in-person observations.

“I think most polar scientists have considered water moving across the surface of Antarctica to be extremely rare. But we found a lot of it, over very large areas,” says Jonathan Kingslake, a glaciologist at Columbia University and one of the authors of the paper, in a statement. The survey also confirms that these ponds and rivers have existed in some form for decades.

The discovery fleshes out some major geographical features of Antarctica, the world’s least mapped land area. Most of the continent was not surveyed until the middle of 1957, when Soviet and Western scientists collaborated on the International Geophysical Year. (Imagine if we suddenly discovered several ponds the length of Rhode Island hidden in North America.)

“There was really so little known about the hydrology of Antarctica,” says Ian Willis, a glaciologist at the Scott Polar Research Institute at Cambridge University who was not connected to the paper. “About 10 years ago, I used to tell the students that there’s just starting to be an understanding of water and the Greenland ice sheet. The same is true of Antarctica today.”

The studies have an importance beyond the science of the world’s least-understood land area. They may require the recalculation of some of the longest-term estimates of sea-level rise, though it is unclear whether those projections will increase or decrease.

Contemporary models of the planet’s snow-and-ice system—the cryosphere—do not account for such an expansive meltwater network in Antarctica. Instead, they assumed that large meltwater ponds would rapidly melt and destroy ice shelves. In 2002, a 12,000-year-old ice shelf called Larsen-B disintegrated in less than six months after large ponds of meltwater formed on its surface. Researchers projected that future ice shelves would meet a similar fate.