A group of Muslim women wearing modest beach wear were harassed by a group of women in northern Italy claiming that they can’t go in the water with their clothing.
This is just prejudice mixed with ridiculousness. Yes covering head to toe seems weird based on western culture. But it doesn't hurt anything at all, there are certainly no hygiene issues. Do these people know what's in the ocean? Everything, that's what, you name it, it's in there. A bit of cloth isn't going to affect the ocean .00000000000001%.
Except... That's not how the ocean works? There are localized effects to pollution. You can test this by spilling oil in your nearest ocean. Watch how it disperses, and watch how it doesn't actually disperse that far away from you because of currents and whatnot.
Not justifying the OP, but your statement is really inaccurate.
How much pollution do you expect to get off a piece of cloth that's presumably been washed versus a regular person's body? Is it really inaccurate to say it isn't a concern pollution wise? Is it worth bringing up in this context? Despite your disclaimer, aren't you giving fuel to the idea that the complaints had some merit?
That's 100% correct though I'd like to add the caveat that you shouldn't swim in clothing -- Burkinis are made for swimming, of course, and they're fine, but the article says nothing about what the woman actually wore, if you're about to go swimming in loose-fitting ordinary cloth yes you should absolutely be stopped.
We got basic rescue swimmer qualifications in school (DLRG Bronze) and part of that was swimming in clothing (in particular, age-old ill-fitting flecktarn they picked up somewhere) and then undressing while in water, it is not easy even if you're a stellar swimmer, if you can barely hold yourself over water without panicking (that's like the default skill level of people who can supposedly swim) you're done for. Doubly so on the fucking beach with waves and undertow and everything.