In 1935, a storm swept through Houston, turning parts of the city into a lake. It was a wake-up call to city officials; they needed to get serious about flood control. About a decade later, the U.S. Army Corps of Engineers finished building two massive reservoirs west and upstream of the city. For the better part of a century, the Addicks and Barker dams have held back water that would have otherwise surged through Buffalo Bayou, the flood-prone waterway that snakes through downtown Houston before dumping into the Ship Channel.

This week, for the second time in as many years, a storm has pushed the Addicks and Barker dams to their limit. Early Monday morning, as Tropical Storm Harvey lingered over Houston and drowned whole swaths of the city, the Army Corps of Engineers began controlled releases from the dams, the first time they’ve done so during a major storm. By Monday afternoon, several neighborhoods near the reservoirs were under voluntary or mandatory evacuation as officials announced that releases from Addicks and Barker would continue for the foreseeable future. By early Tuesday morning, Addicks had topped the dam’s 108-foot spillway, leading to what officials call “uncontrolled releases” from the reservoir. Some homes could be inundated for a month.

Harris County Flood Control District meteorologist Jeff Linder called the releases the least-worst decision officials could make in light of floodwaters that continue to fill the reservoirs faster than they can safely drain. “If you are upstream of the reservoir, the worst is not over,” Linder said at a Monday afternoon press conference, warning that “water is going to be inundating areas that have currently not been inundated.” When someone asked him, via Twitter, whether the dams could break and trigger a Katrina-like disaster, Linder offered a one-word response: “No.”