I guess we should have expected it, really. On May 15 we hiked to Marmari (Μαρμαρι) Beach, a 2 hour round trip on rough, hilly paths (plus half an hour of swimming and beachcombing).
Our reward was nice swimming and the filthiest beach I have ever seen. I don't directly blame anyone.
It seems that certain beaches are just well-positioned to catch every bit of floatsam around, and this is one of them: the litter on the beach was surely not the result of visitors to the beach, as the character of the debris wasn't right: not enough broken liquor bottles, too much stuff that looked like it washed overboard: milk crates, orphaned sandals, broken up plastic bits of just about anything imaginable, what looked like a marine transponder or radio, and so forth.