It would seem to be a child's dream.

For the last 17 years, Lego pieces have been washing up on the shores of Cornwall, England, to the delight of mystified beachgoers.

Except, it's not exactly a mystery. On Feb. 13, 1997, a shipping container filled with nearly 5 million Lego pieces was thrown into the sea when the ship carrying them, the New York-bound Tokio Express, was struck by a huge wave. In all, 62 containers were lost overboard some 20 miles offshore, the BBC reports.

According to Tracey Williams, a British writer who launched a Facebook page — Lego Lost at Sea — to document the Lego discoveries, most of the 4.8 million pieces were nautical-themed: scuba gear, seagrass and spear guns among the plastic dragons and daisies.

"These days the holy grail is an octopus or a dragon," Williams told the BBC. "I only know of three octopuses being found — and one was by me — in a cave in Challaborough, Devon. It's quite competitive. If you heard that your neighbor had found a green dragon, you'd want to go out and find one yourself."

Williams, who founded a local beach-cleaning group, says shipwrecked Lego bits wash up daily. And her Facebook page is littered with Lego findings. On Monday in Perranporth, a Lego scuba tank washed ashore. According to the cargo manifest, there were 97,500 of them in the container that fell off the Tokio Express.

Of the 4.8 million Lego pieces lost overboard, an estimated 3.2 million of them were light enough to have floated to the surface, Williams says.

While confirmed findings from the Lego container have been limited to the U.K. to date, Facebook users around the world have been reporting possible discoveries. Last week, a woman from Australia sent Williams a photo of a Lego flipper found washed ashore in Melbourne "sometime in the last five years."

Dr. Curtis Ebbesmeyer, an oceanographer who's studied the Tokio Express case, wrote, "It's possible that after 17 years, a Lego flipper could have made it to Australia."

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And while the daily Lego discoveries may be a dream for some beachcombers, they're a nightmare for environmentalists.

"If you look at the washed-up Lego, it looks perfect, like it's just come out of the box," Claire Wallerstein, head of a Cornwall beach care group, told the BBC. "Plastic in the sea is not going to just decompose and go away."