It’s called Duckweed a.k.a Wolffia Globosa.
Duckweed is a small flowering plant, known for being the smallest flowing plant in the world with a diameter of 0.1-0.2mm.
It grows in mats on the surface of calm, freshwater, such as ponds, lakes and marshes.
They are commonly considered a pest among ponds and water features as they can multiply rapidly if not regularly maintained.
Don’t get put off by the photos here, you can eat it raw as is common across Asia but you don’t have to eat it like this. I’m told it has a slightly grassy, fresh taste.
Once ground into a powder it is claimed to be a useful alternative to whey powder as it is 68% protein.
With the powder, you can use it in anything that you can usually make with soy or whey powder.
Photos courtesy of Jan Thomas Johansson