Starting on July 14, thousands of yellow blobs started washing ashore on French beaches.
The blobs looked a bit like foam, yellow earwax or mousse.
The yellow blobs washed ashore over the course of several days, along several beaches in the tourist heavy portion of North France.
Not quite foam
The balls have a slightly brittle texture and don't really resemble foam, but though they seem like paraffin, they don't smell like it and don't melt in the sun.
Tons of waste
So far tons of waste has washed up.
Here, a view of the foam tangled up with kelp.
The organization Sea-Mer Association has been trying to clean up the foam, so children don't use it to adorn their sand castles.
Foam balls everywhere
Here, another view of the foam balls tangled with other pollution.
It's not clear what caused the pollution, but one possibility is that grease from hot boat exhaust mixed with cold sea water, creating these clumps
Once the pollution is in the water, it can mix with other contaminants.
So far, officials say the flotsam poses no risk to human health, but people from the Sea-Mer Association say it's not safe to touch until it's identified.