I went to Playa del Carmen a few months ago, and yeah, there was a huge quantity of seaweed. It was still a beautiful place to visit, with lots to do.
They had trucks go up and down the beach scraping it up every morning, but it's something to be aware of.
I haven't been to the beach in a long time. I thought I had seen a lot of that, but never that much. I mean, it's ugly and gross, especially if it touches you in the water. But, what I knew as "normal", the algae comes and go with the tides, and it takes 3 days to a week to clean up all by itself. What you do if you go to a beach and find it full of algae, is keep traveling in one direction until you find a clean beach, or clean enough. OR, you go back a week later if that's an option for you.
Again, I don't know the current conditions in the beaches I used to go.
What I found weird is that the seaweed tends to stay close to the shore, but if you go out, there's no seaweed farther out.
Is seaweed like that good for anything?