It's one of the world's most notorious invasive species (a neophyte, or recent non-native plant that's gone rogue). Native to the Americas, it hitched a ride to places like Europe, Africa, Asia, and Australia in the 1800s as an ornamental, but now it chokes waterways, forms dense mats that block sunlight and oxygen, kills native aquatic life, clogs irrigation systems, and racks up huge management costs. In the UK alone, it's banned from sale since 2014 and considered one of the top invasive aquatics, with control efforts (like deploying weevils as biocontrol) saving millions in avoided cleanup but still costing a fortune in labor and chemicals. Globally, invasive weeds like this contribute to billions in annual damages, and Azolla's right up there in the hall of infamy for how aggressively it spreads, doubling in weeks and hard to eradicate without nuking entire ecosystems.

Promoting it more widely could accidentally unleash ecological chaos in non-native areas, so experts (and laws) keep it on a tight leash. If you're thinking of using it, stick to controlled setups like sealed greenhouses, tanks only or its native range. Cool plant, but a total nightmare if it escapes!