Kelp is rich in iodine, something many people don't get enough of.
Instead we ingest large quantities of nitrates and perchlorates, which can cause thyroid problems, especially in people with an iodine deficiency. The nitrates mostly come from preservatives in meat. The perchlorates mostly come from solid-fuel rockets and runoff from military installations, and are concentrated in the leaves of irrigated salad crops.
To learn more about these problems, here are some articles from google scholar.
Kelp has a high iodine content. The iodine content varies greatly from one sample to the next.
Excessive iodine can aggravate thyroid problems. Tell your doctor what you're doing and don't over do it.
Step 1: Gather Kelp
Only gather kelp that's either drifting freely or has washed up on the beach. If there's current, here's how to tell if kelp is anchored without even touching it: If the "head" is pointing upstream, the kelp is anchored. If the "head" is pointing downstream, it's drifting freely.
If you still see a lot of the stem floating at high tide, the kelp is drifting. At low tide you'll see a lot of stem even on anchored kelp.
Here I am off the coast of Northern California. I found this bunch of kelp drifting in the current.
Put it in a bag or other closed container before you get to the beach, you don't want your kelp to get sandy.
Step 2: Rinse the Kelp
It's easier to wash the sand off in salt water than it is in fresh water.
If you want your dried kelp not to be so salty, rinsing in fresh water will do that.
I like mine salty.
Step 3: Dry the Kelp
Just hang it anywhere there's some airflow and it will dry out.
You might think of hanging it on a clothesline, but...
Step 4: Built in Clothesline
If you find a long piece of kelp, you can just string the whole stem from tree to tree.
The Northwest Coast Natives used to use dried kelp stems as fishing line. If you need to tie two stems together, use a "granny knot". The "granny knot" looks like a square knot done wrong. It's usually a weak and unsafe knot, but is good for tying roots, vines, bark, and other stiff materials that will break if you bend them too far. I learned this from an Ojibway woman while helping to build a birch bark canoe.
Step 5: Dried!
The white stuff on these heads are crystals of salt from the interior.
There are some spots on these leaves, they're eggs from some small sea animal, I eat those too.
Here's my non-scientific method to decide if I need to eat some kelp:
Caffeine stops having much of an affect on me.
I'm getting plenty of sleep, excercise, and sunlight.
I'm getting plenty of iron (anemia runs in my family).
Then I'll nibble a piece of kelp leaf each day for a few days, and usually the caffeine starts working just great!