By the time they knew the danger, the green scum was everywhere.

You know where she is by the green scum on the water.

It was covered with a flat, unbroken expanse of green scum.

That was the payoff - this green scum on the surface.

The green scum formed a solid covering on the surface of the pond.

They never noticed the green scum growing in certain tidal pools.

The green scum under his feet stank, but the smell came from somewhere else.

"Just a little green scum on the water."

Where he stood, the green scum covered the stream for many yards.

There's a pool covered with green scum, and there's some holes around here too.