Where to look

Can someone tell me where I find clay clumps in minecraft because I really have no idea about it

https://minecraft-de.gamepedia.com/...ia.com/Ton

You can find it in rivers or ponds. The block looks so gray

Clay is often available in large quantities, it can be made into many more "decorative" objects.
It can be found under water on the banks (in the river) … You don't have to search deep.