Explanation

Spirogyra is called pond silk because it is very slimy and hence slippery to the touch.

It is a freshwater green algae

They are found in shallow ponds, ditches, and lakes.

They are free-floating.

Additional informational:

Spirogyra's two-layered cell walls are composed of pectin on the outside and cellulose on the inside.

The body of the spirogyra has a shiny and silky texture due to the mucilage

that is produced when this pectin dissolves in water. Pond silk gets its name from this.