The floating ice shelves that buttress Antarctica are less icy than we thought, it turns out. They’re filled with flowing water. New research published in the scientific journal Nature maps the extensive network of meltwater from Antarctica's ice sheets and found that, contrary to previous understanding, lakes and rivers—even waterfalls—created by melting have been common for at least seven decades.

Two new papers analyze satellite imagery of Antarctica dating back to 1973 and aerial photography dating back to 1947 for evidence of meltwater. Warming oceans melt ice shelves around from the bottom up, while warming air temperatures melt them from the top down, creating pools and rivers of liquid water on the continent's surface.

Researchers found that over the last 70 years, a system of meltwater drainage has transported water from the continent of Antarctica across the floating ice shelves that surround it, traveling up to 75 miles and creating ponds up to 50 miles long.

This isn’t great news for the stability of the ice shelf. Water is heavy, and the weight can cause the ice below these lakes to crack. As glaciologist Alison Banwell wrote in a separate analysis of the studies for Nature, “If a lake suddenly drains through a crevasse to the ocean below, the load deficit from the ice shelf’s surface can induce more crevasses, potentially triggering a chain reaction” of draining lakes. “This process might have been responsible for the large-scale break-up of Antarctica’s Larsen B Ice Shelf in 2002, when more than 2000 lakes drained in just a few days.”

All that water ends up in the ocean, contributing to rising sea levels. As NASA geophycisist Ala Khazendar told NPR in January, "Ice shelves are very important. They are the gates of Antarctica in a way, and the gatekeepers of Antarctica." The National Snow and Ice Center estimates that if the Antarctic Ice Shelf—which covers 98 percent of the continent—melted, sea levels would rise by as much as 200 feet.

All that makes meltwater a little worrisome for climate scientists, but there may be a silver lining, at least according to one of the published papers.

One river network the researchers studied ends in a 427-foot-wide waterfall that can empty the entire amount of meltwater produced by the ice shelf annually in just seven days. That may make the ice shelf more stable, since the meltwater gets funneled into the ocean immediately instead of building up on top of the ice shelf and cracking the ice below. “Export of meltwater by surface rivers may buffer the impact of warming temperatures,” the researchers wrote. At least when it comes to breaking up ice sheets. Unfortunately, those drainage systems are still really effective at sloughing off water into the ocean, which will still affect sea level rise.