A gigantic block of brown sargassum seaweed, twice the width of the United States, is currently floating between the Gulf of Mexico and the shore of Western Africa. The 5,000-mile wide tangle is so massive it can even be seen from space, NBC News reports. While sargassum is not an uncommon sight, a mass this large is highly unusual, experts told NBC. Ocean currents are pushing the seaweed west, causing experts to worry it will wash up in clumps across Gulf beaches as well as choke coral and diminish water quality as it begins to rot. “It can really threaten critical infrastructure,” Brian Barnes, an assistant research professor at the University of South Florida’s College of Marine Science, told NBC.