What is the plural for kelp?

The plural of kelp is either kelp or kelps,depending on how you are using it.

Non-count nouns like snow, food, kelp, people, sugar, do not usually need a plural form, but in certain uses they add an 's' to show that they are "groups of groups".

Here are some examples:

"Joe wants chocolate milk and Sue wants soy milk and I use skim milk. There are so many milks available now..."

Lactose, fructose, and other sugars can be found...

We have different nations, different 'races', but the peoples of the world must learn to...

The various shallow-water kelps have ....