Did you accidentally drop your Bolta-Hardrubber comb into the river? They found it.
Or your red Pocketline Swing HD1 mobile telephone? They found that too.
Or your keychain? Yup. They found it.
As part of the construction of the North/South metro line in Amsterdam, engineers drained the historic river, and archaeologists cataloged the objects found at Damrak¹ and Rokin.
You can see the results at belowthesurface.amsterdam (English version).
Even the radioactive toothpaste.
¹ Not to be confused with Darmok, which is something else entirely.