AP Photo/Eduardo Verdugo
In this Sunday, Aug. 5, 2018 photo, children play on the beach full of sargassum in Bahia La Media Luna, near Akumal in Quintana Roo state, Mexico.
Shorelines around Florida and the Caribbean have been choked with invaders over the past month. No, it's not tourists - it's seaweed.
Sargassum seaweed, which originates in the Gulf of Mexico and is actually a type of algae, has been washing up on beaches and coastlines in vacation-heavy hotspots like Miami and Cancun since July.
The weeds have wreaked havoc on local fauna, choking coral reefs and destroying habitats for birds, sea turtles, and fish. The seaweed deluge has also made life difficult for fisherman, since it is capable of wrecking boat propellers, fishing nets, and engines.
Sargassum seaweed is usually pushed by currents into the Sargasso Sea - a large gyre off the coast of North America - where the floating mats serve as an important habitat for marine organisms.
Researchers are struggling to figure out why the weeds have started washing up on Caribbean coastlines. Some experts say the influx of Sargassum could be fueled by a combination of increased nitrogen pollution from agricultural runoff and rising ocean temperatures, according to The New Republic.
In some extreme cases, resorts have had to close beaches during the busy summer season to remove the seaweed. Here's what the invasion looks like: